STT Upgrade Path Prompt

Improve the OpenJibo .NET speech-to-text path for live robot testing.

Current repo context:

workspace root: .\OpenJibo
current live captures from 2026-04-18 showed that some turns succeeded, but many buffered-audio turns failed before producing a usable transcript
the current local .NET STT path is in:
- src/Jibo.Cloud/dotnet/src/Jibo.Cloud.Infrastructure/Audio/LocalWhisperCppBufferedAudioSttStrategy.cs
- src/Jibo.Cloud/dotnet/src/Jibo.Cloud.Infrastructure/Audio/OggOpusAudioNormalizer.cs
- src/Jibo.Cloud/dotnet/src/Jibo.Cloud.Application/Services/WebSocketTurnFinalizationService.cs
- src/Jibo.Cloud/dotnet/src/Jibo.Cloud.Application/Services/DefaultSttStrategySelector.cs
Node remains the oracle for current behavior:
- src/Jibo.Cloud/node/open-jibo-link.js
live test evidence and guidance are documented in:
- docs/development-plan.md
- docs/live-jibo-test-runbook.md
- src/Jibo.Cloud/dotnet/README.md

Observed problems to ground the work:

one captured run could not find whisper-cli at the configured rooted path
many buffered-audio turns failed because ffmpeg rejected the normalized Ogg output
we need a more reliable path for testing than the current partially working local whisper chain

Goals:

review the current .NET STT seam and compare it against the Node preprocessing flow
recommend and implement the best next STT path for testing, preferring reliability and simplicity over novelty
keep the STT integration behind the existing abstractions so we can swap providers later
preserve or improve telemetry so failed turns clearly show whether the problem is decode, tool lookup, provider failure, or unusable transcript quality
update tests and docs to match the chosen direction

Constraints:

do not remove the synthetic transcript-hint path; it is still valuable for fixture replay and parity
do not assume Azure-hosted STT is automatically the answer unless the codebase and testing needs support that choice
prefer an implementation that is easy for other revival-group testers to run consistently
avoid large speculative architecture changes that are not needed for a near-term v1 testable cloud

Deliverables:

code changes for the improved STT path
tests covering strategy selection, success, and failure handling
doc updates with exact setup guidance and a recommendation on whether local whisper remains optional, fallback-only, or deprecated for testing
a short summary of the tradeoffs and why the chosen path is the best next step