M6 + M0: hardening, deploy docs, PoC scripts

- Pipeline-down fallback: dialplan plays gogo-fallback after a failed
  AudioSocket (§15) + script to synthesize the Bosnian prompt via TTS
- Voice heartbeat file → /health/voice endpoint + live status in admin panel
- Retention job also purges stale call registrations; chat sessions metered;
  100%-usage super-admin alert email (GOGO_ADMIN_ALERT_EMAIL)
- .env.example, docs/DEPLOY.md (compose stack, GPU node, backups pg_dump,
  update procedure, security notes)
- §16 Definition of Done as an automated test: softphone-style call → fake
  partner availability → request pushed → webhook confirm → console SMS
- M0 PoC scripts: STT accuracy harness (CER/WER + spoken-digit check; dry-run
  verified with espeak-ng samples + faster-whisper small on CPU — phone number
  extracted exactly), TTS bake-off (Azure vs ElevenLabs, latency+cost), and
  end-to-end latency smoke test speaking real AudioSocket to the live pipeline

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,46 @@
+# Gogo Telefon — copy to .env and fill in. All variables are prefixed GOGO_.
+
+# Core
+GOGO_ENV=prod
+GOGO_SECRET_KEY=change-me-long-random-string        # sessions, action links, secret encryption
+GOGO_BASE_URL=https://app.gogotelefon.ba            # public URL (action links, transcripts, widget)
+GOGO_DATABASE_URL=postgresql+psycopg://gogo:gogo@db:5432/gogo
+GOGO_INTERNAL_TOKEN=change-me-dialplan-token        # Asterisk dialplan ↔ backend
+
+# LLM (agent)
+GOGO_ANTHROPIC_API_KEY=sk-ant-...
+GOGO_LLM_MODEL=claude-haiku-4-5-20251001
+
+# TTS — one of the two (default decided by the Phase-0 bake-off)
+GOGO_TTS_PROVIDER=azure                             # azure | elevenlabs
+GOGO_AZURE_SPEECH_KEY=
+GOGO_AZURE_SPEECH_REGION=westeurope
+GOGO_ELEVENLABS_API_KEY=
+
+# STT (voice service)
+GOGO_WHISPER_MODEL=large-v3                         # small for CPU dev
+GOGO_WHISPER_DEVICE=cuda                            # cuda | cpu | auto
+
+# Email (proposal emails to owners)
+GOGO_EMAIL_PROVIDER=smtp                            # console for dev
+GOGO_SMTP_HOST=mail.example.ba
+GOGO_SMTP_PORT=587
+GOGO_SMTP_USER=
+GOGO_SMTP_PASSWORD=
+GOGO_EMAIL_FROM="Gogo Telefon <noreply@gogotelefon.ba>"
+GOGO_ADMIN_ALERT_EMAIL=                             # super-admin alerts (100% usage)
+
+# SMS (via GSM gateway, M5; console logs SMS in dev)
+GOGO_SMS_PROVIDER=console                           # console | gsm_gateway
+GOGO_GSM_GATEWAY_URL=http://192.168.1.50
+GOGO_GSM_GATEWAY_USER=admin
+GOGO_GSM_GATEWAY_PASSWORD=
+
+# Google Calendar OAuth (free/busy read-only, §8.1)
+GOGO_GOOGLE_CLIENT_ID=
+GOGO_GOOGLE_CLIENT_SECRET=
+
+# Voice pipeline
+GOGO_VOICE_PORT=9092
+GOGO_RECORDINGS_DIR=/data/recordings
+GOGO_AUDIO_RETENTION_DAYS=90