fix(proxy): clear auto-refresh-scheduler tracking state on account removal

AutoRefreshScheduler kept per-account entries in its tracking maps
(lastRefreshResetTime, consecutiveFailures, lastFailureProbeAt,
uncountedProbeFailures) after an account was deleted via the API, since
only its own 60s periodic sweep or full server shutdown pruned them.
Add a public clearAccountTracking() and wire it into account removal
via a register/unregister registry, mirroring the existing refreshClearer
pattern used for token-manager cleanup.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>