Add voice buttons, Wi-Fi netconfig, and demo STT server

demo-server/.env.example

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+# API key expected from the button panel (X-API-Key header)
+API_KEY=97098109-3188-496b-b075-0e8d83c2bef5
+
+# OpenRouter
+OPENROUTER_API_KEY=sk-or-v1-your-key
+OPENROUTER_BASE_URL=https://openrouter.ai/api/v1
+# Whisper-compatible STT model (OpenRouter)
+# Better on short noisy RU: openai/gpt-4o-mini-transcribe or openai/gpt-4o-transcribe
+# Popular but not best here: openai/whisper-large-v3
+STT_MODEL=openai/gpt-4o-mini-transcribe
+# Text classification model
+CLASSIFY_MODEL=openai/gpt-4o-mini
+
+# SOCKS5 proxy for OpenRouter (optional but recommended)
+# Example: socks5://user:pass@host:1080  or  socks5://127.0.0.1:1080
+SOCKS5_PROXY=
+
+# Bind
+HOST=0.0.0.0
+PORT=5000
+
+# If true, skip OpenRouter and return a fake category from filename/heuristics
+MOCK_AI=false
+
+# Profile denoise via post-roll tail. Default off — raw audio works better on panel mics.
+# Set DENOISE=true and voice.postRollMs=700 on the button to enable.
+DENOISE=false
+DENOISE_PROP=0.75