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>

backend/build.rs

@@ -0,0 +1,10 @@
+fn main() {
+    // On Windows, embed the application icon into the .exe
+    // This sets both the Explorer icon and makes it available as a resource
+    #[cfg(target_os = "windows")]
+    {
+        let mut res = winresource::WindowsResource::new();
+        res.set_icon("assets/ironpad.ico");
+        res.compile().expect("Failed to compile Windows resources");
+    }
+}