Provider plugin bundles for OC Chat.
Purpose
-------
Each subdirectory is a self-contained provider implementation.
Importing a subpackage (e.g. ``import providers.deepseek``) triggers
self-registration into ``oc_chat.core.provider_plugin.registry``.
The active provider is selected at startup by the
``OC_CHAT_PROVIDER`` env var (default ``"deepseek"``) and looked up
in that registry.
Responsibilities
----------------
- Mark ``providers/`` as a Python package.
- Hold provider bundles: ``deepseek`` (production) and ``example``
(deterministic stub for templates and tests).
See ``providers/README.md`` (added in Phase C.5) for the canonical
bundle layout.
Diagnostics
-----------
Domain: OC_CHAT.CLIENT
Levels:
L2 — lifecycle events
L3 — semantic details
L4 — deep tracing
Contracts
---------
- Module-level L4 ``_dbg`` is a diagnostics-coverage marker; it
emits nothing at default verbosity (domain default is L2).
- Subpackages self-register on import — never import here, only at
the call site that needs the provider active.
Dependencies
------------
- oc_diagnostics (structured debug logging via _dbg)
1.15.0