fix(cliproxy): avoid credential cooldown for connection-lifecycle disconnect errors

- Added a dedicated `connection_lifecycle` error code and lifecycle detection for context cancellation, EOF variants, and websocket close conditions.
- Introduced shared gating (`shouldSkipCredentialCooldown`) so transport/session lifecycle failures do not mark auth/model as unavailable or set retry cooldown.
- Kept request-scoped/invalid failures as high-priority and preserved status-bearing HTTP errors behavior so auth cooldown still applies when appropriate.

Closes: #4819 #4787