On gateway restart, persisted non-terminal calls are now verified with
the provider (Twilio/Plivo/Telnyx) before being restored to memory.
This prevents phantom calls from blocking the concurrent call limit.
- Add getCallStatus() to VoiceCallProvider interface
- Implement for all providers with SSRF-guarded fetch
- Transient errors (5xx, network) keep the call with timer fallback
- 404/known-terminal statuses drop the call
- Restart max-duration timers for restored answered calls
- Skip calls older than maxDurationSeconds or without providerCallId
