feat(07-01): Alembic migration 0005 + SystemSettings ORM model
- Add backend/migrations/versions/0005_system_settings.py (revision 0005, down_revision 0004)
- Creates system_settings table with 9 columns: id (UUID PK gen_random_uuid()), provider_id (String NOT NULL UNIQUE), api_key_enc (Text NULL), base_url (Text NULL), model_name (Text NOT NULL default ''), context_chars (Integer NOT NULL default 8000), is_active (Boolean NOT NULL default false), created_at/updated_at (TIMESTAMPTZ default now())
- UniqueConstraint uq_system_settings_provider_id on provider_id
- Add SystemSettings ORM model to backend/db/models.py following CloudConnection style
- downgrade() drops system_settings table cleanly
curo1305
4eb317749f