Add models caching and management functionality with corresponding API endpoints and templates

Co-authored-by: Copilot <copilot@github.com>

backend/app/db.py

@@ -75,6 +75,17 @@ def _run_migrations(conn: duckdb.DuckDBPyConnection) -> None:
             created_at   TIMESTAMP DEFAULT now()
         )
     """)
+    conn.execute("""
+        CREATE TABLE IF NOT EXISTS models_cache (
+            id             UUID      DEFAULT uuid() PRIMARY KEY,
+            model_id       VARCHAR   NOT NULL UNIQUE,
+            name           VARCHAR   NOT NULL,
+            modality       VARCHAR   NOT NULL,
+            context_length BIGINT,
+            pricing        JSON,
+            fetched_at     TIMESTAMP NOT NULL
+        )
+    """)
     _seed_admin(conn)