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

[Siumauricio]

Problem

@dokploy/server gets bundled several times into the same server process: an inline copy in dist/server.mjs (esbuild + tsconfig paths for subpath imports), the compiled node_modules copy (bare imports left external by packages: "external"), and 4 copies duplicated across .next/server/chunks by transpilePackages. Every module-level side effect runs once per copy:

• Up to 6 postgres.js pools per process — db/index.ts explicitly skipped the globalThis cache in production (measured: 21 idle connections on a fresh instance after ~20 min of traffic)
• 6 dockerode clients, and the repeated Using Docker socket log at boot (7 times)
• 6 independent better-auth instances

On top of that, the image keeps pnpm resident as a process wrapper (~100MB RSS doing nothing). Measured container usage: ~930MB after 27 minutes up (801MB node + 99MB pnpm).

Changes

• db/index.ts: use the globalThis cache in production too → one pool per process
• constants/index.ts: cache the dockerode client on globalThis → also fixes the repeated socket logs
• lib/auth.ts: wrap betterAuth() in a createBetterAuth() factory and cache the instance on globalThis
• Dockerfile: exec node directly in CMD instead of going through pnpm start

Note: the auth.ts diff is almost entirely indentation from the factory wrap — review with whitespace hidden (git diff -w / hide whitespace on GitHub, real diff is +16/−2).

Code copies are still duplicated across bundles (drizzle schema instantiated per copy); deduplicating the bundling itself (serverExternalPackages in prod + wildcard exports to dist/) is a follow-up.