fix(proxy): clear pending-rotation, codex-model, and exhaustion caches on account removal

Three account-keyed in-memory Maps had no TTL and no per-account clear
wired into account removal: pending-rotation-registry's refresh-token
rotation map, codex-model-catalog's last-known-good model listing, and
model-capacity's negative exhaustion cache. Each now clears its entry
for the removed account inside createAccountRemoveHandler, alongside
the existing token-manager/auto-refresh-scheduler cleanup.

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