fix: make STT config env-overridable and fix doc issues

Code fixes:
- STT model, Groq base URL, and OpenAI STT base URL are now
  configurable via env vars (STT_GROQ_MODEL, STT_OPENAI_MODEL,
  GROQ_BASE_URL, STT_OPENAI_BASE_URL) instead of hardcoded
- Gateway and Discord VC now read stt.model from config.yaml
  (previously only CLI did this — gateway always used defaults)

Doc fixes:
- voice-mode.md: move Web UI troubleshooting to web.md (was duplicated)
- voice-mode.md: simplify "How It Works" for end users (remove NaCl,
  DAVE, RTP internals)
- voice-mode.md: clarify STT priority (OpenAI used first if both keys
  set, Groq recommended for free tier)
- voice-mode.md: document new STT env overrides in config reference
- web.md: remove duplicate Quick Start / Step 1-3 sections
- web.md: add mobile HTTPS mic workarounds (moved from voice-mode.md)
- web.md: clarify STT fallback order

tools/transcription_tools.py

@@ -32,13 +32,13 @@ from typing import Optional, Dict, Any, Tuple
 logger = logging.getLogger(__name__)
 
 
-# Default STT models per provider
-DEFAULT_STT_MODEL = "whisper-1"
-DEFAULT_GROQ_STT_MODEL = "whisper-large-v3-turbo"
+# Default STT models per provider (overridable via env)
+DEFAULT_STT_MODEL = os.getenv("STT_OPENAI_MODEL", "whisper-1")
+DEFAULT_GROQ_STT_MODEL = os.getenv("STT_GROQ_MODEL", "whisper-large-v3-turbo")
 
-# Provider endpoints
-GROQ_BASE_URL = "https://api.groq.com/openai/v1"
-OPENAI_BASE_URL = "https://api.openai.com/v1"
+# Provider endpoints (overridable via env for proxies / self-hosted)
+GROQ_BASE_URL = os.getenv("GROQ_BASE_URL", "https://api.groq.com/openai/v1")
+OPENAI_BASE_URL = os.getenv("STT_OPENAI_BASE_URL", "https://api.openai.com/v1")
 
 
 def _resolve_stt_provider() -> Tuple[Optional[str], Optional[str], str]: