feat(asr): add local Whisper fallback and desktop voice input

[IRONICBo]

Summary

• bundle a sherpa-onnx OfflineWhisper worker using the fixed Whisper small multilingual int8 model and Silero VAD
• use the same ASR router for Desktop microphone input and site video/audio transcription
• route signed-in accounts with an active paid subscription and remaining credits to managed cloud ASR
• route logged-out, unpaid, expired, depleted, BYOK, and wallet-check-failure cases to local Whisper small
• expose transcribe_audio to every account so the selected cloud/local route is actually usable

Desktop voice input

• add microphone recording to the Desktop composer using mono 16 kHz PCM WAV with strict RIFF, size, format, alignment, and two-minute validation
• append successful transcripts to the active composer without submitting them automatically
• display the backend-selected route and live local model download progress
• fall back to local ASR only when cloud access is rejected before upload (401, 402, or 403), avoiding duplicate provider work or billing
• make the persistent local worker cancellation-safe so an interrupted request cannot leave a stale response for the next transcription

Model lifecycle and packaging

• keep the model fixed to Whisper small; there is no low, medium, or high selector
• download the pinned 376,129,181-byte model only on first local use, verify byte lengths and SHA-256 digests, then install atomically
• serialize installation across processes, clean stale staging directories, and reuse one persistent helper process
• include socai-asr beside socai in Desktop sidecars and macOS/Windows CLI release archives
• document source installation of both socai and socai-asr

Scope

• no new server change or server PR is required; managed ASR continues to use the existing server contract
• TikTok remains independent in feat(tiktok): add site-native research tools #286
• Douyin remains independent in feat(dy): complete site-native research tools #285
• no shared content-platform abstraction is introduced

Validation

• cargo test -p socai-core --lib: 100 passed, 0 failed, 2 ignored
• cargo test -p socai_app --lib: 3 passed, 0 failed
• cargo check --workspace --all-targets
• cargo check -p socai-asr
• pnpm --dir app build
• git diff --check
• isolated source installation produced executable socai and socai-asr binaries in the same bin directory
• a real 20-second Douyin audio clip completed local Whisper small transcription and returned a Chinese transcript
• two read-only Codex review passes completed; cloud-access race, source packaging, worker cancellation, route display, progress display, and repository-test-policy findings were addressed

[vercel]

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