fix(models): sync local selections across account mode

[EF1874]

Summary

• synchronize the full selected local/BYOK Agent model set between account and local modes on login and logout
• sync the local fallback model back into account mode after all account BYOK models were cleared, while preserving a valid local default
• refresh the canonical model catalog after authentication and during authenticated startup so stale projections are repaired immediately
• preserve mode-isolated model assignments, embedding selection, and newer account sessions during logout races

Verification

• Backend account/model/runtime tests: 53 passed
• Migration suite: 116 passed
• Frontend model/login/settings/auth tests: 114 passed
• Backend lint and typecheck passed
• Desktop production build passed