feat: extend init_data to load and sync user_agent_catalog

- Add UserAgentCatalogSeed and UserAgentCatalogYaml Pydantic models
- Add load_user_agent_catalog function to load from YAML
- Add _upsert_user_agent_catalog helper for upsert logic
- Add initialize_user_agent_catalog function for initialization
- Refactor initialize_data to call initialize_llm_catalog and initialize_user_agent_catalog
- Fix UserAgentCatalog.llm_id type from str to uuid.UUID

backend/src/models/user_agent_catalog.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import uuid
+
 from sqlalchemy import ForeignKey, String
 from sqlalchemy.dialects.postgresql import JSONB, UUID
 from sqlalchemy.orm import Mapped, mapped_column
@@ -14,7 +16,7 @@ class UserAgentCatalog(TimestampMixin, Base):
         String(20),
         primary_key=True,
     )
-    llm_id: Mapped[str] = mapped_column(
+    llm_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("llms.id", ondelete="RESTRICT"),
         nullable=False,