docs: Add detailed UI components for Phase 4.1 auto-update system

- Add 4.1.2 section for update manager UI
- Specify all dialogs (checking, available, downloading, install, failed, no updates)
- Include status bar integration with update indicators
- Define menu structure for Help menu updates
- Add background behavior specifications
- List async/non-blocking implementation requirements
- Include UI testing acceptance criteria

DEVELOPMENT_PLAN.md

@@ -801,6 +801,95 @@ AUTO_UPDATE_NOTIFY=true
 
 ---
 
+#### 4.1.2 Update UI Components (`src/webdrop_bridge/ui/update_manager_ui.py`)
+
+**Menu Integration:**
+```
+Help Menu
+├─ Check for Updates...     (manual trigger)
+├─ ─────────────────────
+└─ About WebDrop Bridge     (show current version)
+```
+
+**Dialogs:**
+
+1. **"Checking for Updates..." Dialog**
+   - Animated spinner/progress
+   - "Cancel" button
+   - Message: "Checking for updates..."
+   - Timeout: 10 seconds
+
+2. **"Update Available" Dialog**
+   - Current version: X.X.X
+   - New version: Y.Y.Y
+   - Changelog/release notes (scrollable)
+   - Buttons: "Update Now", "Later", "Skip This Version"
+   - Checkbox: "Show next update reminder"
+
+3. **"Downloading Update..." Dialog**
+   - Progress bar (download %)
+   - File size info: "Downloading 195 MB..."
+   - "Cancel Download" button
+   - Cancel option reverts to "Later"
+
+4. **"Install & Restart?" Dialog**
+   - Message: "Update downloaded and ready to install"
+   - Buttons: "Install Now", "Install on Next Restart"
+   - Checkbox: "Save my work before installing"
+   - Shows warning if unsaved changes exist
+
+5. **"No Updates Available" Dialog**
+   - Message: "You're running the latest version (X.X.X)"
+   - Button: "OK"
+   - Optional: "Check again" button
+
+6. **"Update Failed" Dialog**
+   - Error message with reason
+   - Buttons: "Retry", "Download Manually", "OK"
+   - Manual download link to Forgejo releases
+
+**Status Bar Integration:**
+```
+┌─────────────────────────────────────┐
+│ Ready  🔄 Checking for updates...  │  (during check)
+│ Ready  ✅ Update available (v1.1.0) │  (when found)
+│ Ready  ⬇️ Downloading update (45%)  │  (during download)
+└─────────────────────────────────────┘
+```
+
+**Background Behavior:**
+- Startup: Check for updates automatically (no UI blocking)
+- If newer version found: Show notification badge on Help menu
+- Silent background download when user is idle
+- Notification when download complete
+- Prompt for restart when convenient
+
+**Implementation:**
+- Signal/slot architecture for async operations
+- Non-blocking UI (all operations async)
+- Graceful degradation if network unavailable
+- Thread pool for download operations
+- Cancel-safe download handling
+
+**Deliverables:**
+- [ ] `src/webdrop_bridge/ui/update_manager_ui.py` - UI dialogs
+- [ ] Update menu item integration
+- [ ] Status bar update indicator
+- [ ] All dialogs with error handling
+- [ ] Tests for UI interactions
+
+**Acceptance Criteria:**
+- Menu item works and triggers check
+- All dialogs display correctly
+- Progress shown during download
+- Restart options work
+- Network errors handled gracefully
+- Cancel operations work safely
+- Status bar updates in real-time
+- No blocking operations on main thread
+
+---
+
 ### 4.2 Enhanced Logging & Monitoring
 
 **Deliverables:**