Database operator commands for the orchestration registry.
Purpose
-------
Expose read-only database health commands beneath
``python -m oc_chat.registry db``.
Responsibilities
----------------
- Wire the ``db integrity-check`` command.
- Reserve future database operation names with explicit v0.2.x stubs.
- Format structured integrity reports for humans or JSON consumers.
Diagnostics
-----------
Domain: OC_CHAT.MAIN
Levels:
L2 - lifecycle events
L3 - semantic details
L4 - deep tracing
Contracts
---------
- ``integrity-check`` does not mutate logical registry state.
- Reserved commands exit 2 with a clear not-implemented message.
Dependencies
------------
- oc_diagnostics (structured debug logging via _dbg)
- oc_chat.registry.backends.sqlite (SQLite backend)
- oc_chat.registry.discovery (registry path discovery)