Refactor settings system and improve context initialization

Backend:
- Add type validation and coercion for settings API
- Implement SettingStorage and SettingType in registry
- Improve CRUD operations for settings

Frontend:
- Refactor Theme, Language, Sidebar, ViewMode contexts
- Simplify admin components (GeneralTab, SettingsTab, UsersTab)
- Add new settings endpoints to API client
- Improve App initialization flow

Infrastructure:
- Update Dockerfile and docker-compose.yml
- Add .dockerignore
- Update Makefile and README

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

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

docker-compose.yml

@@ -11,7 +11,7 @@ services:
     ports:
       - "5174:8000"
     healthcheck:
-      test: [ "CMD-SHELL", "curl -f http://localhost:8000/health || exit 1" ]
+      test: [ "CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:8000/health')" ]
       interval: 30s
       timeout: 10s
       start_period: 40s