Fix Database.initialize and remove invalid theme param

- Add initialize() method as alias for connect()
- Remove invalid tab_nav_background_fill theme parameter

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

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

src/storage/database.py

@@ -183,6 +183,10 @@ class Database:
 
         logger.info(f"Database connected: {self.db_path}")
 
+    async def initialize(self) -> None:
+        """Alias for connect() for compatibility."""
+        await self.connect()
+
     async def close(self) -> None:
         """Close database connection."""
         if self._connection: