feat: implement update management web UI

Add complete update management interface to web UI:
- Update status display (current version, last status, timestamp, errors)
- Check for updates button with availability indicator
- Apply update button with confirmation dialog and backup warnings
- Rollback button with confirmation dialog
- Update logs viewer (collapsible, reverse chronological)
- Auto-refresh after update/rollback actions (5s delay)

Features:
- Uses existing Pico CSS framework for consistent styling
- Integrates with existing auth system (Bearer token/session cookies)
- Real-time feedback with loading states and error handling
- German UI language matching existing interface
- All API calls use existing api() helper function

Complete US_000029-033 and TASK_000030-034:
- US_000029: Display update status in web UI
- US_000030: Trigger update check from UI
- US_000031: Apply updates from UI
- US_000032: Display update logs in UI
- US_000033: Trigger rollback from UI

EPIC_000008 (Client-Side Update Mechanism) now fully complete.
Documentation updated per SOP (CHANGELOG, PROJECT_STATUS, stories/tasks).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -38,6 +38,7 @@ By: Codex (GPT-5)
 | 29.12.2025 | ⚙️ Code | ID: Update-Models und Settings erweitert (Models, Status-File Paths). By: Codex (GPT-5) |
 | 29.12.2025 | ⚙️ Code | ID: Rollback-Script hinzugefuegt (scripts/rollback_client.sh). By: Codex (GPT-5) |
 | 30.12.2025 | ⚙️ Code | ID: Update-API Endpunkte implementiert (GET /update/status, POST /update/check, POST /update/apply, POST /update/rollback, GET /update/logs). By: Claude Sonnet 4.5 |
+| 30.12.2025 | ⚙️ Code | ID: Update-UI im Web-Frontend implementiert (Status-Anzeige, Check/Apply/Rollback Buttons, Logs-Viewer). By: Claude Sonnet 4.5 |
 
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