Release v0.2.0: Task comments, recurring calendar, system tray, app branding

New features:
- Task comments with date-stamped entries and last-comment summary
- Recurring tasks expanded on calendar (daily/weekly/monthly/yearly)
- System tray mode replacing CMD window (Windows/macOS/Linux)
- Ironpad logo as exe icon, tray icon, favicon, and header logo

Technical changes:
- Backend restructured for dual-mode: dev (API-only) / prod (tray + server)
- tray-item crate for cross-platform tray, winresource for icon embedding
- Calendar view refactored with CalendarEntry interface for recurring merging
- Added CHANGELOG.md, build-local.ps1, version bumped to 0.2.0

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/index.html

@@ -6,6 +6,8 @@
     <meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate" />
     <meta http-equiv="Pragma" content="no-cache" />
     <meta http-equiv="Expires" content="0" />
+    <link rel="icon" href="/favicon.ico" type="image/x-icon" />
+    <link rel="apple-touch-icon" href="/logo-180.png" />
     <title>Ironpad</title>
     <script>
       // Apply saved theme immediately to prevent flash