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>

backend/app/main.py

@@ -138,16 +138,17 @@ async def startup_event():
     # Seed default settings from registry
     from sqlalchemy.orm import Session
     from app import crud
-    from app.core.settings_registry import get_database_defaults
+    from app.core.settings_registry import SettingScope, get_database_settings
 
     with Session(engine) as db:
-        # Get all database settings with defaults from registry
-        default_settings = get_database_defaults()
+        # Seed only GLOBAL database settings with defaults from registry
+        for setting_def in get_database_settings():
+            if setting_def.scope != SettingScope.GLOBAL:
+                continue
 
-        for key, value in default_settings.items():
-            if crud.settings.get_setting(db, key) is None:
-                logger.info(f"Seeding default setting: {key}={value}")
-                crud.settings.update_setting(db, key, value)
+            if crud.settings.get_setting(db, setting_def.key) is None:
+                logger.info(f"Seeding default setting: {setting_def.key}={setting_def.default}")
+                crud.settings.update_setting(db, setting_def.key, setting_def.default)
 
 
 # Shutdown event