Implement Alembic for database migrations and update FastAPI initialization

- Integrate Alembic for managing database schema migrations, replacing the previous SQL schema management.
- Update the FastAPI application to synchronize interface definitions at startup.
- Modify the Docker Compose command to run Alembic migrations before starting the API.
- Enhance the Makefile with new commands for database migration and revision management.
- Remove outdated SQL schema and seed files, transitioning to a more dynamic migration approach.
- Add initial migration scripts and configuration for Alembic, ensuring a structured database evolution.

backend/db/models.py

@@ -73,6 +73,7 @@ class KnowledgeBase(Base):
     embedding_model_resource_id: Mapped[str | None] = mapped_column(
         String(40),
         ForeignKey("model_resources.id", ondelete="SET NULL"),
+        index=True,
         nullable=True,
     )
     status: Mapped[str] = mapped_column(String(16), default="active")  # active|archived