## Why
Azure Speech post-stream refinement can improve final segment quality while preserving the existing low-latency streaming transcription flow.

## What Changes
- Add an `AzureSpeech.PostProcessingOption` setting.
- Keep the default option unset while the live Azure backend uses `ConversationTranscriber`.
- Apply the configured option only for compatible Azure Speech SDK recognizer paths; skip it for `ConversationTranscriber` to preserve working live diarized transcription.
- Use a Speech resource region that supports post-stream refinement.

## Impact
- Affected specs: `meeting-transcription`
- Affected code: Azure Speech options, Azure streaming transcription provider, appsettings, Azure provider tests