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/components/StatsDisplay.svelte

@@ -14,7 +14,6 @@
   <div class="stats-row">
     <span class="stat-label">Messages:</span>
     <span class="stat-value">{$formattedStats.messagesSession}</span>
-    <span class="stat-secondary">/ {$formattedStats.messagesTotal}</span>
   </div>
 
   <div class="stats-section">
@@ -32,11 +31,6 @@
       <span class="stat-label">Output:</span>
       <span class="stat-value">{$formattedStats.sessionOutputTokens}</span>
     </div>
-    <div class="stat-row stat-highlight">
-      <span class="stat-label">Total:</span>
-      <span class="stat-value">{$formattedStats.totalTokens}</span>
-      <span class="stat-cost">{$formattedStats.totalCost}</span>
-    </div>
   </div>
 
   <div class="stats-section">
@@ -44,17 +38,14 @@
     <div class="stat-row">
       <span class="stat-label">Code blocks:</span>
       <span class="stat-value">{$formattedStats.codeBlocksSession}</span>
-      <span class="stat-secondary">/ {$formattedStats.codeBlocksTotal}</span>
     </div>
     <div class="stat-row">
       <span class="stat-label">Files edited:</span>
       <span class="stat-value">{$formattedStats.filesEditedSession}</span>
-      <span class="stat-secondary">/ {$formattedStats.filesEditedTotal}</span>
     </div>
     <div class="stat-row">
       <span class="stat-label">Files created:</span>
       <span class="stat-value">{$formattedStats.filesCreatedSession}</span>
-      <span class="stat-secondary">/ {$formattedStats.filesCreatedTotal}</span>
     </div>
   </div>
 
@@ -128,14 +119,6 @@
     opacity: 0.8;
   }
 
-  .stat-highlight {
-    font-weight: 600;
-    color: var(--accent-primary);
-    margin-top: 0.25rem;
-    padding-top: 0.25rem;
-    border-top: 1px solid var(--border-color);
-  }
-
   .stat-label {
     color: var(--text-secondary, #9ca3af);
   }