feat(deploy): production Docker + Caddy stack for OpenRouter

[NabilRFG12]

Summary

Adds a turnkey self-hosted deployment path for a VPS, using OpenRouter as the LLM provider.

• docker-compose.prod.yml — runs the app behind Caddy with automatic Let's Encrypt HTTPS; app is not exposed directly (only :80/:443 via Caddy), with a healthcheck on /api/health and persistent volumes for app data + Caddy certs.
• Caddyfile — reverse-proxies to openmaic:3000, reads {$DOMAIN} / {$ACME_EMAIL} from env; streams SSE (e.g. /api/chat) and uses no proxy timeouts so long generations (maxDuration = 300) aren't cut off.
• .env.openrouter.example — OpenRouter-focused template (OPENROUTER_API_KEY, OPENROUTER_MODELS, DEFAULT_MODEL=openrouter:…, ACCESS_CODE, DOMAIN, ACME_EMAIL) with commented-out TTS/image/video slots.
• .gitignore — track the new .env.openrouter.example (mirrors the existing !.env.example exception).

Notes

• OPENROUTER_MODELS replaces the 2 built-in OpenRouter entries; the Settings UI surfaces any listed slug as selectable (lib/store/settings.ts fetchServerProviders), and the key stays server-side (isServerConfigured).
• OpenRouter is LLM-only; without a TTS/image provider the app degrades gracefully (browser Web Speech voice, no generated slide images).
• The build compiles native deps (sharp, @napi-rs/canvas) — needs ~2GB+ RAM.
• No real secrets committed — placeholders only.

Test plan

• cp .env.openrouter.example .env.local; set DOMAIN, ACME_EMAIL, OPENROUTER_API_KEY, ACCESS_CODE
• docker compose -f docker-compose.prod.yml up --build -d on a VPS with a domain + ports 80/443 open
• Caddy obtains a valid TLS cert; site loads over HTTPS and prompts for the access code
• In Settings, OpenRouter shows as server-configured with the OPENROUTER_MODELS list selectable
• Generate a classroom end-to-end (outline → scenes); confirm playback + a discussion (SSE) works through the proxy
• HTTP-only fallback: set DOMAIN=:80 and confirm the app serves without a cert

https://claude.ai/code/session_01TnEDwUuc2k9PvgRmHLGrfB

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