Add admin commands for database operations

Features:
- Add admin command group for database operations
- admin list-users: List all users from SQLite/PostgreSQL/MySQL
- admin user-notes: List notes for specific user
- Add CodiMDDatabase class for direct DB access

cli_anything/codimd/core/user.py

@@ -113,3 +113,20 @@ class UserManager:
             raise Exception(f"Failed to get avatar: {response.status_code}")
 
         return response.content
+
+    def list_all_users(self) -> list:
+        """List all users (admin only).
+
+        This requires direct database access as CodiMD doesn't expose
+        a user list API. You'll need to provide database configuration.
+        """
+        # Since CodiMD doesn't have a built-in user list API,
+        # we return a note explaining this limitation
+        raise NotImplementedError(
+            "CodiMD doesn't have a built-in API to list all users. "
+            "This feature requires direct database access. "
+            "You can query the database directly:\n"
+            "  PostgreSQL: SELECT id, email, profile FROM Users;\n"
+            "  MySQL: SELECT id, email, profile FROM Users;\n"
+            "  SQLite: SELECT id, email, profile FROM Users;"
+        )