Add Deepgram transcription provider

[Jorel97]

Summary

• add a Deepgram transcription provider for Sapat's current provider registry
• support DEEPGRAM_API_KEY plus endpoint/model/format/diarization/punctuation env flags
• add mocked request/response coverage and document the Deepgram env block

Validation

• python -m compileall sapat tests
• python -m pytest tests/providers/test_group_a.py tests/test_registry.py tests/test_cli.py -q (50 passed)
• python -m black --check sapat/providers/deepgram.py tests/providers/test_group_a.py
• git diff --check
• Full python -m pytest tests -q currently reports 181 passed and 1 unrelated Windows path failure in tests/providers/test_group_d.py::TestWhisperXProvider::test_transcribe_builds_command_and_reads_output because WHISPERX_BINARY loses path separators before validation.

No secrets, audio files, generated transcripts, or payout details are included.

[Jorel97]

Update: added explicit Deepgram registry and CLI coverage after the initial PR.

Additional validation now passing locally:

• python -m pytest tests/providers/test_group_a.py tests/test_registry.py tests/test_cli.py -q (52 passed)
• python -m black --check sapat/providers/deepgram.py tests/providers/test_group_a.py tests/test_registry.py tests/test_cli.py
• python -m compileall sapat tests
• git diff --check

The current Continue status checks are reporting Agent encountered an error rather than a project test failure. I do not see maintainer feedback requiring code changes yet.