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/lib/stores/conversations.ts

@@ -9,6 +9,7 @@ import type {
 import type { CharacterState } from "$lib/types/states";
 import { cleanupConversationTracking } from "$lib/tauri";
 import { characterState } from "$lib/stores/character";
+import { sessionsStore } from "$lib/stores/sessions";
 
 export interface Conversation {
   id: string;
@@ -287,6 +288,9 @@ function createConversationsStore() {
         return false;
       }
 
+      // Cancel any pending auto-save for this conversation
+      sessionsStore.cancelAutoSave(id);
+
       // Clean up tracking for this conversation (including temp files)
       await cleanupConversationTracking(id);
 
@@ -434,6 +438,8 @@ function createConversationsStore() {
         if (conv) {
           conv.terminalLines.push(line);
           conv.lastActivityAt = new Date();
+          // Schedule auto-save for this conversation
+          sessionsStore.scheduleAutoSave(conv);
         }
         return convs;
       });
@@ -462,6 +468,8 @@ function createConversationsStore() {
         if (conv) {
           conv.terminalLines.push(line);
           conv.lastActivityAt = new Date();
+          // Schedule auto-save for this conversation
+          sessionsStore.scheduleAutoSave(conv);
         }
         return convs;
       });