feat: add native clipboard support for screenshot paste (#67)

## Summary
- Adds Tauri clipboard-manager plugin to read images from native clipboard
- Falls back to native clipboard when WebView clipboard API returns empty (fixes screenshot paste)
- Allows sending messages with just attachments (no text required)
- Logs attached files to output with 📎 emoji

## Test plan
- [ ] Build and run the app natively on Windows
- [ ] Copy a screenshot (Win+Shift+S) and paste in the chat input
- [ ] Verify the screenshot appears as an attachment preview
- [ ] Send the attachment and verify Claude receives the file path
- [ ] Test sending a message with only an attachment (no text)
- [ ] Verify the 📎 log line shows the attached filename

**Note:** Paste will not work in WSLg dev environment due to clipboard isolation - needs native Windows build to test.

✨ This PR was created with help from Hikari~ 🌸

Co-authored-by: Hikari <hikari@nhcarrigan.com>
Reviewed-on: #67
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src-tauri/src/commands.rs

@@ -1,3 +1,4 @@
+use std::path::PathBuf;
 use tauri::{AppHandle, State};
 use tauri_plugin_http::reqwest;
 use tauri_plugin_store::StoreExt;
@@ -6,6 +7,7 @@ use crate::achievements::{get_achievement_info, load_achievements, AchievementUn
 use crate::bridge_manager::SharedBridgeManager;
 use crate::config::{ClaudeStartOptions, HikariConfig};
 use crate::stats::UsageStats;
+use crate::temp_manager::SharedTempFileManager;
 
 const CONFIG_STORE_KEY: &str = "config";
 
@@ -298,3 +300,83 @@ pub async fn check_for_updates() -> Result<UpdateInfo, String> {
         release_notes: latest.body.clone(),
     })
 }
+
+#[derive(Debug, Clone, serde::Serialize)]
+pub struct SavedFileInfo {
+    pub path: String,
+    pub filename: String,
+}
+
+#[tauri::command]
+pub async fn save_temp_file(
+    temp_manager: State<'_, SharedTempFileManager>,
+    conversation_id: String,
+    data: Vec<u8>,
+    filename: Option<String>,
+) -> Result<SavedFileInfo, String> {
+    let mut manager = temp_manager.lock();
+    let path = manager.save_file(&conversation_id, &data, filename.as_deref())?;
+
+    let filename = path
+        .file_name()
+        .map(|n| n.to_string_lossy().to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+
+    Ok(SavedFileInfo {
+        path: path.to_string_lossy().to_string(),
+        filename,
+    })
+}
+
+#[tauri::command]
+pub async fn register_temp_file(
+    temp_manager: State<'_, SharedTempFileManager>,
+    conversation_id: String,
+    file_path: String,
+) -> Result<(), String> {
+    let mut manager = temp_manager.lock();
+    manager.register_file(&conversation_id, PathBuf::from(file_path));
+    Ok(())
+}
+
+#[tauri::command]
+pub async fn get_temp_files(
+    temp_manager: State<'_, SharedTempFileManager>,
+    conversation_id: String,
+) -> Result<Vec<String>, String> {
+    let manager = temp_manager.lock();
+    let files = manager.get_files_for_conversation(&conversation_id);
+    Ok(files.iter().map(|p| p.to_string_lossy().to_string()).collect())
+}
+
+#[tauri::command]
+pub async fn cleanup_temp_files(
+    temp_manager: State<'_, SharedTempFileManager>,
+    conversation_id: String,
+) -> Result<(), String> {
+    let mut manager = temp_manager.lock();
+    manager.cleanup_conversation(&conversation_id)
+}
+
+#[tauri::command]
+pub async fn cleanup_all_temp_files(
+    temp_manager: State<'_, SharedTempFileManager>,
+) -> Result<(), String> {
+    let mut manager = temp_manager.lock();
+    manager.cleanup_all()
+}
+
+#[tauri::command]
+pub async fn cleanup_orphaned_temp_files(
+    temp_manager: State<'_, SharedTempFileManager>,
+) -> Result<usize, String> {
+    let mut manager = temp_manager.lock();
+    manager.cleanup_orphaned_files()
+}
+
+#[tauri::command]
+pub async fn get_file_size(file_path: String) -> Result<u64, String> {
+    let metadata = std::fs::metadata(&file_path)
+        .map_err(|e| format!("Failed to get file metadata: {}", e))?;
+    Ok(metadata.len())
+}