feat: add multiple productivity features and UI enhancements (#68)

## Summary

This PR adds a collection of productivity features and UI enhancements to improve the Hikari Desktop experience:

### New Features
- **Clipboard History** (#25) - Track and manage copied code snippets with language detection, search, filtering, and pinning
- **Quick Actions Panel** (#15) - Buttons for common quick actions like "Review PR", "Run tests", "Explain file", with customizable actions
- **Git Integration Panel** (#24) - View current branch, changed/staged files, quick git actions (commit, push, pull), and branch management
- **Session Import/Export** (#8) - Export conversations to JSON and import previously saved sessions
- **Snippet Library** (#22) - Save and reuse common prompts with categories and quick insert
- **Session History** (#14) - Auto-save conversations with browsable history and search
- **High Contrast Mode** (#20) - Accessibility theme with improved visibility
- **Minimize to System Tray** (#11) - System tray support with right-click menu

### UI Enhancements
- Trans-pride gradient theme applied across UI elements
- Copy button added to code blocks
- Linter formatting and eslint-disable comments for cleaner code

## Closes

Closes #8
Closes #11
Closes #14
Closes #15
Closes #20
Closes #22
Closes #24
Closes #25
Closes #34
Closes #35
Closes #36
Closes #37
Closes #69
Closes #70

## Test Plan

- [ ] Verify clipboard history captures code from code block copy buttons
- [ ] Verify clipboard history captures manually selected text from terminal
- [ ] Test snippet library CRUD operations and insertion
- [ ] Test quick actions panel with default and custom actions
- [ ] Test git panel shows correct status, branch, and performs git operations
- [ ] Test session history auto-save and restore
- [ ] Test session import/export roundtrip
- [ ] Verify high contrast mode provides adequate contrast
- [ ] Test minimize to tray functionality and tray menu
- [ ] Verify trans-pride gradient theme displays correctly in all themes

---
*✨ This PR was created with help from Hikari~ 🌸*

Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Reviewed-on: #68
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src-tauri/src/clipboard.rs

@@ -0,0 +1,259 @@
+// Clipboard history module for tracking and managing copied code snippets
+// Implements issue #25 - Clipboard History feature
+
+use serde::{Deserialize, Serialize};
+use std::sync::Mutex;
+use tauri_plugin_store::StoreExt;
+use uuid::Uuid;
+
+const STORE_FILE: &str = "hikari-clipboard.json";
+const HISTORY_KEY: &str = "clipboard_history";
+const MAX_HISTORY_SIZE: usize = 100;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ClipboardEntry {
+    pub id: String,
+    pub content: String,
+    pub language: Option<String>,
+    pub source: Option<String>,
+    pub timestamp: String,
+    pub is_pinned: bool,
+}
+
+impl ClipboardEntry {
+    pub fn new(content: String, language: Option<String>, source: Option<String>) -> Self {
+        Self {
+            id: Uuid::new_v4().to_string(),
+            content,
+            language,
+            source,
+            timestamp: chrono::Utc::now().to_rfc3339(),
+            is_pinned: false,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+struct ClipboardHistory {
+    entries: Vec<ClipboardEntry>,
+}
+
+// Track last clipboard content to avoid duplicates
+#[derive(Default)]
+struct ClipboardState {
+    last_content: Option<String>,
+}
+
+static CLIPBOARD_STATE: Mutex<ClipboardState> = Mutex::new(ClipboardState { last_content: None });
+
+fn load_history(app: &tauri::AppHandle) -> ClipboardHistory {
+    let store = app.store(STORE_FILE).ok();
+    store
+        .and_then(|s| s.get(HISTORY_KEY))
+        .and_then(|v| serde_json::from_value(v.clone()).ok())
+        .unwrap_or_default()
+}
+
+fn save_history(app: &tauri::AppHandle, history: &ClipboardHistory) -> Result<(), String> {
+    let store = app.store(STORE_FILE).map_err(|e| e.to_string())?;
+    store.set(
+        HISTORY_KEY,
+        serde_json::to_value(history).map_err(|e| e.to_string())?,
+    );
+    store.save().map_err(|e| e.to_string())?;
+    Ok(())
+}
+
+/// List all clipboard entries, optionally filtered by language
+#[tauri::command]
+pub fn list_clipboard_entries(
+    app: tauri::AppHandle,
+    language: Option<String>,
+) -> Result<Vec<ClipboardEntry>, String> {
+    let history = load_history(&app);
+    let entries = if let Some(lang) = language {
+        history
+            .entries
+            .into_iter()
+            .filter(|e| e.language.as_ref() == Some(&lang))
+            .collect()
+    } else {
+        history.entries
+    };
+    Ok(entries)
+}
+
+/// Capture current clipboard content and add to history
+#[tauri::command]
+pub fn capture_clipboard(
+    app: tauri::AppHandle,
+    content: String,
+    language: Option<String>,
+    source: Option<String>,
+) -> Result<ClipboardEntry, String> {
+    // Check for duplicate (same content as last capture)
+    {
+        let mut state = CLIPBOARD_STATE.lock().map_err(|e| e.to_string())?;
+        if state.last_content.as_ref() == Some(&content) {
+            // Return existing entry if content is the same
+            let history = load_history(&app);
+            if let Some(entry) = history.entries.first() {
+                if entry.content == content {
+                    return Ok(entry.clone());
+                }
+            }
+        }
+        state.last_content = Some(content.clone());
+    }
+
+    let entry = ClipboardEntry::new(content, language, source);
+    let mut history = load_history(&app);
+
+    // Add to front of history
+    history.entries.insert(0, entry.clone());
+
+    // Enforce max size (keep pinned entries)
+    let mut pinned: Vec<ClipboardEntry> = history
+        .entries
+        .iter()
+        .filter(|e| e.is_pinned)
+        .cloned()
+        .collect();
+    let mut unpinned: Vec<ClipboardEntry> = history
+        .entries
+        .into_iter()
+        .filter(|e| !e.is_pinned)
+        .collect();
+
+    // Trim unpinned entries if over max size
+    if unpinned.len() + pinned.len() > MAX_HISTORY_SIZE {
+        let max_unpinned = MAX_HISTORY_SIZE.saturating_sub(pinned.len());
+        unpinned.truncate(max_unpinned);
+    }
+
+    // Merge back, pinned first then unpinned
+    pinned.extend(unpinned);
+    history.entries = pinned;
+
+    // Sort by timestamp descending (newest first), pinned entries stay at top
+    history.entries.sort_by(|a, b| {
+        if a.is_pinned && !b.is_pinned {
+            std::cmp::Ordering::Less
+        } else if !a.is_pinned && b.is_pinned {
+            std::cmp::Ordering::Greater
+        } else {
+            b.timestamp.cmp(&a.timestamp)
+        }
+    });
+
+    save_history(&app, &history)?;
+    Ok(entry)
+}
+
+/// Delete a clipboard entry by ID
+#[tauri::command]
+pub fn delete_clipboard_entry(app: tauri::AppHandle, id: String) -> Result<(), String> {
+    let mut history = load_history(&app);
+    history.entries.retain(|e| e.id != id);
+    save_history(&app, &history)?;
+    Ok(())
+}
+
+/// Toggle pin status of an entry
+#[tauri::command]
+pub fn toggle_pin_clipboard_entry(
+    app: tauri::AppHandle,
+    id: String,
+) -> Result<ClipboardEntry, String> {
+    let mut history = load_history(&app);
+    let entry = history
+        .entries
+        .iter_mut()
+        .find(|e| e.id == id)
+        .ok_or("Entry not found")?;
+
+    entry.is_pinned = !entry.is_pinned;
+    let updated_entry = entry.clone();
+
+    // Re-sort to move pinned entries to top
+    history.entries.sort_by(|a, b| {
+        if a.is_pinned && !b.is_pinned {
+            std::cmp::Ordering::Less
+        } else if !a.is_pinned && b.is_pinned {
+            std::cmp::Ordering::Greater
+        } else {
+            b.timestamp.cmp(&a.timestamp)
+        }
+    });
+
+    save_history(&app, &history)?;
+    Ok(updated_entry)
+}
+
+/// Clear all non-pinned entries
+#[tauri::command]
+pub fn clear_clipboard_history(app: tauri::AppHandle) -> Result<(), String> {
+    let mut history = load_history(&app);
+    history.entries.retain(|e| e.is_pinned);
+    save_history(&app, &history)?;
+    Ok(())
+}
+
+/// Search clipboard entries by content
+#[tauri::command]
+pub fn search_clipboard_entries(
+    app: tauri::AppHandle,
+    query: String,
+) -> Result<Vec<ClipboardEntry>, String> {
+    let history = load_history(&app);
+    let query_lower = query.to_lowercase();
+    let entries = history
+        .entries
+        .into_iter()
+        .filter(|e| {
+            e.content.to_lowercase().contains(&query_lower)
+                || e.language
+                    .as_ref()
+                    .is_some_and(|l| l.to_lowercase().contains(&query_lower))
+                || e.source
+                    .as_ref()
+                    .is_some_and(|s| s.to_lowercase().contains(&query_lower))
+        })
+        .collect();
+    Ok(entries)
+}
+
+/// Get all unique languages from history
+#[tauri::command]
+pub fn get_clipboard_languages(app: tauri::AppHandle) -> Result<Vec<String>, String> {
+    let history = load_history(&app);
+    let mut languages: Vec<String> = history
+        .entries
+        .iter()
+        .filter_map(|e| e.language.clone())
+        .collect();
+    languages.sort();
+    languages.dedup();
+    Ok(languages)
+}
+
+/// Update the language of an entry
+#[tauri::command]
+pub fn update_clipboard_language(
+    app: tauri::AppHandle,
+    id: String,
+    language: Option<String>,
+) -> Result<ClipboardEntry, String> {
+    let mut history = load_history(&app);
+    let entry = history
+        .entries
+        .iter_mut()
+        .find(|e| e.id == id)
+        .ok_or("Entry not found")?;
+
+    entry.language = language;
+    let updated_entry = entry.clone();
+
+    save_history(&app, &history)?;
+    Ok(updated_entry)
+}