refactor(drivers): delete the inert driver-tier recycle machinery (#522)

The tier system was documented, operator-authorable, and inert. Deleted rather than activated,
because its premise is gone rather than merely unused.

"Tier C" meant a driver running out-of-process behind an IDriverSupervisor that could restart its
Host without tearing down the OPC UA session. No such process exists anywhere: Galaxy reaches
MXAccess over gRPC to the external mxaccessgw sidecar (PR 7.2 retired the in-process
Galaxy.Host/Proxy/Shared projects) and FOCAS has run in-process since its managed wire client
landed 2026-04-24. Consistently, IDriverSupervisor had ZERO implementations and there was nothing
for one to implement against.

The issue understated the inertness. It says the Tier-C-only protections never engaged, implying
the Tier A/B parts did. They did not: nothing constructs MemoryTracking, MemoryRecycle or
ScheduledRecycleScheduler outside their own unit tests, so the whole Core/Stability recycle layer
was dead — meaning option (a), "pass real tiers", was never a flag flip. It would have meant
writing the wiring that never existed AND arming it.

Deleted: MemoryTracking, MemoryRecycle, ScheduledRecycleScheduler, IDriverSupervisor, the
vestigial DriverTypeRegistry (referenced only by its own tests), and the RecycleIntervalSeconds
knob — which the AdminUI let an operator author and the parser validated while it configured
nothing.

DriverTier itself SURVIVES and is load-bearing: DriverResilienceOptions.GetTierDefaults supplies
the real per-capability timeout/retry/breaker policies via DriverFactoryRegistry.GetTier and
DriverCapabilityInvokerFactory. Only the isolation-and-recycle layer above it is gone.

Deliberately NOT deleted:

- WedgeDetector came along in the same directory and is equally dead in production, but it is
  tier-agnostic and is not recycle machinery — it only shares the folder. Restored rather than
  swept up in a decision that was not about it.
- IDriver.GetMemoryFootprint() and FlushOptionalCachesAsync() lose their only consumer here.
  Removing them touches all 12 drivers and every test stub, so they are documented as
  consumerless and filed as #525 instead of buried in this diff.

Compatibility: a deployed ResilienceConfig blob still carrying "recycleIntervalSeconds" parses
cleanly (unknown keys are ignored — guarded by a new test, because a blob that suddenly failed to
parse would fall back to tier defaults and silently discard the operator's real overrides), and
the AdminUI's preserve-unknown-keys bag keeps the key rather than rewriting stored config on an
unrelated edit.

The 01/U-6 knob-inertness guard carried an explicit carve-out admitting RecycleIntervalSeconds was
dormant and out of scope; that carve-out is now gone, so the expected set is literally what the
test's name claims.

Note: Host.IntegrationTests has 2 failures (DriverProbeRegistrationTests.is_idempotent,
PrimaryGateFailoverTests) — verified pre-existing by reproducing both on clean master dc9d947b.

Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo

docs/README.md

@@ -26,7 +26,7 @@ The project was originally called **LmxOpcUa** (a single-driver Galaxy/MXAccess
 | [OpcUaServer.md](OpcUaServer.md) | Top-level server architecture — Core, driver dispatch, Config DB, generations |
 | [AddressSpace.md](AddressSpace.md) | `GenericDriverNodeManager` + `ITagDiscovery` + `IAddressSpaceBuilder` |
 | [ReadWriteOperations.md](ReadWriteOperations.md) | OPC UA Read/Write → `CapabilityInvoker` → `IReadable`/`IWritable` |
-| [DriverLifecycle.md](DriverLifecycle.md) | Server-side driver lifecycle + infrastructure contracts (`IDriverFactory`, `IDriverProbe`, `IDriverSupervisor`, `IDriverHealthPublisher`, `IDriverConfigEditor`, `IHistorianDataSource`) + the Commons library |
+| [DriverLifecycle.md](DriverLifecycle.md) | Server-side driver lifecycle + infrastructure contracts (`IDriverFactory`, `IDriverProbe`, `IDriverHealthPublisher`, `IDriverConfigEditor`, `IHistorianDataSource`) + the Commons library |
 | [Subscriptions.md](v1/Subscriptions.md) | Monitored items → `ISubscribable` + per-driver subscription refcount (v1 archive) |
 | [AlarmTracking.md](AlarmTracking.md) | `IAlarmSource` + `AlarmSurfaceInvoker` + OPC UA alarm conditions — native Galaxy alarms end-to-end (live) |
 | [AlarmTracking.md](v1/AlarmTracking.md) | Original alarm-tracking write-up (v1 archive) |