Refactor Workflow and Chat Architecture (#68)

* refactor: overhaul workflow and chat architecture

- Separate Chat and Workflow API endpoints and database models
- Use JSONB to store workflow execution context in Postgres
- Convert workflow engine to use pydantic-ai execution graphs inside a Ray task
- Update frontend React components to support standalone workflow creation
- Remove obsolete and broken workflow runner tests

Co-authored-by: zhaoxi826 <198742034+zhaoxi826@users.noreply.github.com>

* refactor: overhaul workflow and chat architecture

- Separate Chat and Workflow API endpoints and database models
- Use JSONB to store workflow execution context in Postgres
- Convert workflow engine to use pydantic-ai execution graphs inside a Ray task
- Update frontend React components to support standalone workflow creation
- Remove obsolete and broken workflow runner tests

Co-authored-by: zhaoxi826 <198742034+zhaoxi826@users.noreply.github.com>

* refactor: overhaul workflow and chat architecture

- Separate Chat and Workflow API endpoints and database models
- Use JSONB to store workflow execution context in Postgres
- Convert workflow engine to use pydantic-ai execution graphs inside a Ray task
- Update frontend React components to support standalone workflow creation
- Move workflow_engine inside workflow package to keep core root clean
- Remove obsolete and broken workflow runner tests

Co-authored-by: zhaoxi826 <198742034+zhaoxi826@users.noreply.github.com>

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: zhaoxi826 <198742034+zhaoxi826@users.noreply.github.com>

tests/core/postgres_database/postgres_test.py

@@ -82,4 +82,6 @@ async def test_postgres_database(
         mock_conn.run_sync.assert_called_once_with(mock_create_all)
 
     assert await db.get_user_authority(user_id="123") == "test_auth"
+
+
 # noqa: E402