- Added `DailyTransport.send_dtmf()` to expose the Daily call client's DTMF sending capability, enabling applications to send tones during a call (e.g. IVR navigation).
- Added `DailyOutputDTMFFrame` and `DailyOutputDTMFUrgentFrame` frames for sending DTMF through the Daily transport pipeline. Both carry explicit `tones`, `session_id` and `digit_duration_ms` fields that are forwarded to Daily's `send_dtmf` as `tones`, `sessionId` and `digitDurationMs`. When the Daily transport processes these frames, the inherited `button` and `transport_destination` fields are ignored.