[codex] Improve voice input quality pipeline

[neta-zjj]

Summary

• add session-level ASR observability for the websocket voice path: stable request/session ids, structured summary logs, OpenTelemetry session spans, stop reasons, provider/client timing, audio/result counts, and experiment metadata without logging raw audio or transcript text
• add configurable Volc ASR endpoint experiments with stable hash bucketing, plus a local real-Volc experiment script that streams 16k mono PCM in configurable frames instead of uploading one blob
• add optional OpenAI-compatible final-result rewrite for ASR cleanup; it is disabled by default and only runs when ASR_REWRITE_ENABLED=true and an API key is configured
• extend SDK voice events with transcript metadata, alternatives, stop reasons, and client-side telemetry; keep legacy callback usage compatible
• keep AudioWorklet-first capture, browser speech cleanup constraints, improved resampling, and client VAD endpoint stop
• add web composer controls for local voice terms, continuous dictation, candidate replacement, undo, and press-and-hold hotkey release stop
• feed local terms, current composer context, model name, prompt names, and mentions into ASR hotwords/context for the current session
• fix SDK build reproducibility by adding the unrun peer needed by tsdown, and fix the API typecheck path mapping for @cohub/core/content/sanitize

Validation

• pnpm --filter @cohub/gateway typecheck
• pnpm --filter @cohub/gateway test
• pnpm --filter @cohub/gateway lint
• pnpm --filter @cohub/gateway build
• pnpm --filter @neta-art/cohub typecheck
• pnpm --filter @neta-art/cohub exec tsx --test tests/voice-input.test.ts
• pnpm --filter @neta-art/cohub build (passes; existing zod d.ts bundling warnings remain)
• PUBLIC_COHUB_ENV=dev PUBLIC_API_ORIGIN=http://localhost:8787 PUBLIC_GATEWAY_ORIGIN=http://localhost:8788 pnpm --filter web typecheck
• PUBLIC_COHUB_ENV=dev PUBLIC_API_ORIGIN=http://localhost:8787 PUBLIC_GATEWAY_ORIGIN=http://localhost:8788 pnpm --filter web lint
• PUBLIC_COHUB_ENV=dev PUBLIC_API_ORIGIN=http://localhost:8787 PUBLIC_GATEWAY_ORIGIN=http://localhost:8788 pnpm --filter web build (passes; existing large chunk warnings remain)
• pnpm --filter @cohub/api typecheck
• PUBLIC_COHUB_ENV=dev PUBLIC_API_ORIGIN=http://localhost:8787 PUBLIC_GATEWAY_ORIGIN=http://localhost:8788 pnpm -r typecheck
• git diff --check

Notes

• No online/dev Cohub environment was contacted for functional testing.
• No real Volc ASR experiment was run because VOLC_ASR_API_KEY and VOLC_ASR_EXPERIMENT_AUDIO are not configured locally; the experiment script is implemented and exits unless both are provided.
• LLM rewrite remains off by default and will not make external calls without explicit rewrite config and key.