feat: add Docker configuration and environment setup for backend and frontend

.env.example

@@ -0,0 +1,44 @@
+# Copy this file to .env and fill in the values before running `docker compose up`.
+
+# ── Ports (optional, defaults shown) ─────────────────────────────────────────
+BACKEND_PORT=3000
+FRONTEND_PORT=3001
+
+# ── Auth ──────────────────────────────────────────────────────────────────────
+# Generate: openssl rand -hex 32
+JWT_SECRET=change-me-generate-with-openssl-rand-hex-32
+
+# Generate: openssl rand -base64 64
+COOKIE_SECRET=change-me-must-be-at-least-64-characters-long-for-production!!
+
+JWT_EXPIRY_HOURS=24
+
+# Set to true when serving over HTTPS
+SECURE_COOKIE=false
+PRODUCTION=false
+
+# ── CORS ──────────────────────────────────────────────────────────────────────
+# Origin(s) from which the browser will hit the backend, comma-separated.
+# Must match what users type in their browser for the frontend.
+# Example (local):  http://localhost:3001
+# Example (remote): https://tv.example.com
+CORS_ALLOWED_ORIGINS=http://localhost:3001
+
+# ── Frontend / API URL ────────────────────────────────────────────────────────
+# Public URL of the BACKEND, as seen from the user's browser.
+# This is baked into the Next.js client bundle at build time.
+# Example (local):  http://localhost:3000/api/v1
+# Example (remote): https://api.example.com/api/v1
+NEXT_PUBLIC_API_URL=http://localhost:3000/api/v1
+
+# ── Jellyfin ──────────────────────────────────────────────────────────────────
+JELLYFIN_BASE_URL=http://jellyfin:8096
+JELLYFIN_API_KEY=your-jellyfin-api-key-here
+JELLYFIN_USER_ID=your-jellyfin-user-id-here
+
+# ── Database pool (optional) ──────────────────────────────────────────────────
+DB_MAX_CONNECTIONS=5
+DB_MIN_CONNECTIONS=1
+
+# ── PostgreSQL (optional, uncomment db service in compose.yml first) ──────────
+# POSTGRES_PASSWORD=change-me