providers: raise quota exhaustion before fallback
Classify Gemini CLI quota signals from stderr or stdout as QuotaExhaustedError, tear down the CLI process group on every exit path, and let provider generic handlers re-raise quota errors so talent fallback can handle them. Cortex now treats only terminal error events as stream-ending, allowing the pre-fallback quota event to be broadcast without closing the active fallback run.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>