refactor: Migrate database service to SQLModel and Alembic.

- Add SQLModel for type-safe database models
- Implement Alembic for schema migration management
- Create 7 migrations covering all existing schema changes
- Add automatic migration system that runs on startup
- Maintain backward compatibility with existing raw SQL queries
- Remove old manual migration system
- All tests pass (109 tests)

Benefits:
- Full type safety with Pydantic validation
- Version-controlled schema changes
- Automatic migration detection and application
- Better developer experience with typed models

pyproject.toml

@@ -36,6 +36,8 @@ dependencies = [
     "httpx>=0.28.1",
     "pydantic>=2.0.0,<3",
     "boto3>=1.35.0,<2",
+    "sqlmodel>=0.0.25",
+    "alembic>=1.16.5",
 ]
 
 [project.urls]