feat: all-in-one production deployment with install script

Redesign deployment as a single docker-compose with Backspace, Caddy
(auto-HTTPS), and LiveKit (voice/video) using hybrid networking:
Backspace+Caddy on isolated bridge, LiveKit on host mode for WebRTC.

- Add install.sh: interactive installer that handles Docker setup,
  domain/DNS verification, secret generation, LiveKit config, and
  deployment with health-check wait
- Add Caddyfile: static reverse proxy config using Caddy env vars,
  routes /livekit/* to host-mode LiveKit via host.docker.internal
- Rewrite docker-compose.yml: all-in-one with profiles (voice),
  no external volumes/networks, bind mount ./data for visibility
- Fix livekit.ts: use LIVEKIT_URL env var directly instead of
  Host-header derivation that made the env var dead code
- Fix Dockerfile: health check reads $PORT dynamically
- Update .env.example: add DOMAIN, COMPOSE_PROFILES documentation
- Update .gitignore: add livekit.yaml (contains secrets)

.env.example

@@ -1,22 +1,30 @@
-# Backspace Configuration
-# Copy this file to .env and fill in the values
+# ─── Backspace Configuration ────────────────────────────────
+# Copy to .env and configure, or run ./install.sh to generate automatically.
 
-# Server
+# Your server's public domain name (required)
+DOMAIN=example.com
+
+# ─── Server ─────────────────────────────────────────────────
 PORT=3000
 HOST=0.0.0.0
 
-# Authentication — generate a random secret: openssl rand -hex 32
-JWT_SECRET=change_me_to_a_random_64_char_hex_string
+# Authentication — generate with: openssl rand -hex 32
+JWT_SECRET=
 
-# LiveKit Voice/Video (optional — leave empty to disable voice features)
+# Registration — set to false to close signups after initial setup
+REGISTRATION_OPEN=true
+
+# Max file upload size in bytes (default: 100MB)
+MAX_UPLOAD_SIZE=104857600
+
+# ─── LiveKit Voice/Video ───────────────────────────────────
+# To enable voice/video, fill in all three values below and add:
+#   COMPOSE_PROFILES=voice
+# Leave empty to run Backspace without voice features.
 LIVEKIT_URL=
 LIVEKIT_API_KEY=
 LIVEKIT_API_SECRET=
 
-# Storage
-UPLOAD_DIR=./data/uploads
-DB_PATH=./data/backspace.db
-MAX_UPLOAD_SIZE=104857600
-
-# Registration — set to false to disable new user registration
-REGISTRATION_OPEN=true
+# ─── Docker Compose ────────────────────────────────────────
+# Uncomment to enable the LiveKit service:
+# COMPOSE_PROFILES=voice