feat: Docker self-hosting setup

- Fix Dockerfiles to copy pnpm-lock.yaml (frozen-lockfile compliance)
- Add migrate target to API Dockerfile using builder stage
- Add migrate service to docker-compose that runs before API starts
- Add AUTH_DISABLED env var bypass to auth middleware for dev/Docker
- Proxy /api/ from nginx to API container (no CORS needed)
- Include initial Drizzle migration (0000_colossal_colossus.sql)
- Add .env.example with all configurable variables
- Update README with Docker self-hosting instructions

Closes #7

Co-authored-by: Groom Book CTO <cto@groombook.app>
Co-authored-by: Paperclip <noreply@paperclip.ing>

.env.example

@@ -0,0 +1,16 @@
+# Groom Book — Environment Variables
+# Copy this file to .env and adjust values for your deployment.
+
+# ── Database ──────────────────────────────────────────────────────────────────
+DATABASE_URL=postgres://groombook:groombook@postgres:5432/groombook
+
+# ── Authentication ────────────────────────────────────────────────────────────
+# Set AUTH_DISABLED=true to skip OIDC validation (useful for local dev/Docker).
+# In production, configure an Authentik instance and set these values.
+AUTH_DISABLED=false
+OIDC_ISSUER=https://authentik.example.com
+OIDC_AUDIENCE=groombook
+
+# ── API ───────────────────────────────────────────────────────────────────────
+PORT=3000
+CORS_ORIGIN=http://localhost:8080