Add wtf_transcribe link for WTF transcription

[howethomas]

Note

Medium Risk
Adds a new link that fetches/decodes audio (including file:// and remote URLs) and sends it to an external transcription service, then persists derived analysis back to Redis; failures or misconfiguration could impact processing and introduces new outbound network/file access paths.

Overview
Adds a new wtf_transcribe link that scans vCon dialogs, extracts audio from body (base64/base64url) or url (including file:///HTTP), POSTs it to a configurable vfun /transcribe endpoint (optional bearer api-key, diarize, timeout), and writes back a generated WTF-compliant wtf_transcription analysis entry per dialog.

The link skips non-recording dialogs, dialogs below min-duration, and dialogs already containing a wtf_transcription, and includes documentation for configuration, chain usage, and expected output format.

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str(True) produces "True" not "true" for API

Medium Severity

Python's str(True) returns "True" (capital T), not "true". The diarize form field sent to the vfun server will be "True" instead of the expected lowercase "true". Note that the adjacent block field on line 284 correctly uses the lowercase string literal "true", making this inconsistency especially likely to cause issues. Most HTTP APIs parse boolean strings as lowercase, so diarization may silently fail to activate.