Migrate from Fly.io to docker-server (img.pq.io)

- Add infra/docker-compose.yml, deploy-stack.sh, .env.example
- Remove Fly.io GitHub Actions workflow
- Build via EC2, deploy via Portainer + Caddy on Hetzner

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -4,12 +4,18 @@ node_modules/
 # Environment / secrets
 .env
 .env.*
+!.env.example
+!infra/.env.example
+infra/.deploy-secrets
 
 # Logs
 npm-debug.log*
 yarn-error.log*
 pnpm-debug.log*
 
+# Claude memory
+memory/
+
 # OS / editor junk
 .DS_Store
 .vscode