feat: speech-to-text for pi via NVIDIA Speech NIM realtime ASR

- asr_transcribe / asr_health tools + the /asr command, with live partials,
  per-word timings, transcript export and TUI rendering
- zero-dependency realtime client (https + Node 22 global WebSocket):
  mint transcription session -> subprotocol handshake -> event loop -> quiescence
- decodes anything ffmpeg supports (and native 16k mono/stereo pcm16/pcm_f32le wav)
  to the 16 kHz mono PCM16 the NIM mandates
- credentials via ASR_API_KEY / ASR_NIM_URL or ~/.pi/agent/asr.json; never in source
- README documents the six places the published API reference diverges from the
  deployed protocol (commit vs done, cumulative deltas, double .completed,
  HTTP 403 at upgrade, ?token= not rejected, model reset on session.update)

.gitignore

@@ -0,0 +1,10 @@
+node_modules/
+package-lock.json
+yarn-error.log
+*.wav
+*.pcm
+*.mp3
+*.mp4
+asr.json
+.DS_Store
+*.log