refactor(supervise): fold Supervise into the facade as Supervisor; drop dead flat-fallbacks

Move the `Supervise` lifecycle out of its own `orchestrator/supervisor/
supervise.py` and into the package `__init__`, renaming the class to
`Supervisor`. Callers now import it from `bot_bottle.orchestrator.supervisor`
alongside the queue surface it belongs with.

Remove the dead `try/except ImportError` flat-import fallbacks from the
package-only store modules (db_store, audit_store, config_store, queue_store)
and image_cache. Those fallbacks existed for when the store files were
flat-copied into the gateway; post-PRD-0070 the data plane never opens the DB,
so these modules are only ever imported as part of the package. The two gateway
data-plane files that may still be loaded flat (egress_addon_core,
git_gate_render) keep their fallbacks.

Full unit suite green (2251).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_supervise.py

@@ -352,7 +352,7 @@ class TestToolConstants(unittest.TestCase):
         )
 
 
-class _StubSupervise(supervise.Supervise):
+class _StubSupervise(supervise.Supervisor):
     """Concrete Supervise subclass for testing the prepare template."""
 
     def start(self, plan):  # type: ignore