perf: share db, docker and auth singletons across duplicated bundles

The @dokploy/server modules get bundled multiple times per process
(esbuild inline copy, compiled node_modules copy, and several Next.js
chunks via transpilePackages), so every module-level side effect ran
once per copy: up to 6 postgres pools, 6 dockerode clients and 6
better-auth instances in the server process, plus the repeated
'Using Docker socket' logs at boot.

- db/index.ts: use the globalThis cache in production too (one pool per process)
- constants/index.ts: cache the dockerode client on globalThis
- lib/auth.ts: wrap betterAuth() in a factory and cache the instance
- Dockerfile: exec node directly instead of leaving pnpm resident (~100MB RSS)

packages/server/src/constants/index.ts

@@ -81,7 +81,17 @@ const getDockerConfig = (): Docker => {
 	return new Docker({ ...versionOption });
 };
 
-export const docker = getDockerConfig();
+// Igual que db: el módulo se evalúa una vez por copia bundleada, el cache
+// evita crear un cliente (y loguear la detección del socket) por cada una.
+const globalForDocker = globalThis as unknown as {
+	docker?: Docker;
+};
+
+if (!globalForDocker.docker) {
+	globalForDocker.docker = getDockerConfig();
+}
+
+export const docker = globalForDocker.docker;
 
 export const paths = (isServer = false) => {
 	const BASE_PATH =