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>

project-management/requirements/stories/US_000030.md

@@ -1,9 +1,9 @@
-ID: US_000030 | Version: 0.1.0 | Status: Draft
+ID: US_000030 | Version: 0.1.0 | Status: Done
 By: Codex (GPT-5)
 
 # US_000030: Update-Check im Web-UI ausloesen
 
-Status: In Progress
+Status: Done
 
 Als Admin moechte ich manuell nach Updates suchen koennen, damit ich Updates sofort pruefen kann.