Add auto-update feature with Gitea release checking

- Add UpdateChecker class to query Gitea API for latest releases
- Show update dialog with release notes when new version available
- Open browser to release page for download (handles large files)
- Allow users to skip specific versions or defer updates
- Add "Check for Updates Now" button in settings
- Check automatically on startup (respects 24-hour interval)
- Pre-configured for repo.anhonesthost.net/streamer-tools

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

config/default_config.yaml

@@ -73,3 +73,12 @@ remote_processing:
   server_url: ""  # WebSocket URL of remote transcription service (e.g., ws://your-server:8765/ws/transcribe)
   api_key: ""  # API key for authentication
   fallback_to_local: true  # Fall back to local processing if remote fails
+
+updates:
+  auto_check: true  # Check for updates on startup
+  gitea_url: "https://repo.anhonesthost.net"  # Base URL of Gitea server
+  owner: "streamer-tools"  # Repository owner/organization name
+  repo: "local-transcription"  # Repository name
+  skipped_versions: []  # List of versions the user chose to skip
+  last_check: ""  # ISO timestamp of last update check
+  check_interval_hours: 24  # Hours between automatic update checks