fix: address PR review round 4 — remove web UI, fix audio/import/interface issues

Remove web UI gateway (web.py, tests, docs, toolset, env vars, Platform.WEB
enum) per maintainer request — Nous is building their own official chat UI.

Fix 1: Replace sd.wait() with polling pattern in play_audio_file() to prevent
indefinite hang when audio device stalls (consistent with play_beep()).

Fix 2: Use importlib.util.find_spec() for faster_whisper/openai availability
checks instead of module-level imports that trigger heavy native library
loading (CUDA/cuDNN) at import time.

Fix 3: Remove inspect.signature() hack in _send_voice_reply() — add **kwargs
to Telegram send_voice() so all adapters accept metadata uniformly.

Fix 4: Make session loading resilient to removed platform enum values — skip
entries with unknown platforms instead of crashing the entire gateway.

website/docs/user-guide/features/voice-mode.md

@@ -478,10 +478,6 @@ The bot requires an @mention by default in server channels. Make sure you:
 - Edge TTS (free, no key) is the default fallback
 - Check logs for TTS errors
 
-### Web UI issues (firewall, mobile mic)
-
-See the [Web UI Troubleshooting](../messaging/web.md#troubleshooting) guide for firewall, HTTPS, and mobile microphone issues.
-
 ### Whisper returns garbage text
 
 The hallucination filter catches most cases automatically. If you're still getting phantom transcripts: