refactor(backend): rename consolidated_launch -> infra_launch (0081 review)

Mechanical rename addressing review 6141 on #519: "consolidated launch" was
unclear about what it composes. Rename the per-backend module
`consolidated_launch.py` -> `infra_launch.py` and the error
`ConsolidatedLaunchError` -> `InfraLaunchError` across all three backends and
their callers/tests. Unify the three identical per-backend error classes into
one `InfraLaunchError` defined in `backend/base.py` (re-exported by each
`infra_launch`) so the base backend can raise and catch a single shared type —
groundwork for the base owning the gateway-attach flow.

Add a glossary entry defining **infra** = the per-host gateway + orchestrator
service pair every bottle attaches to.

No behavior change.

Refs #516, #519.

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

bot_bottle/backend/base.py

@@ -264,6 +264,12 @@ PlanT = TypeVar("PlanT", bound=BottlePlan)
 CleanupT = TypeVar("CleanupT", bound=BottleCleanupPlan)
 
 
+class InfraLaunchError(RuntimeError):
+    """A per-host infra (gateway + orchestrator) launch/reconcile step could not
+    complete. Shared across backends so the base backend can raise + catch one
+    type; each backend's ``infra_launch`` module re-exports it."""
+
+
 @dataclass(frozen=True)
 class BottleImages:
     """Resolved image references (or artifact paths) for a bottle launch.