Add production compose stack and stop idle load in containers

The development stack was running permanently on a server: polling file
watchers, a healthcheck that rendered a full page every five seconds and no
memory limit grew next dev to 10 GB and pushed the host into swap.

- add compose.prod.yaml running compiled output in separate api/web services
- make the Dockerfile multi-stage with dev and prod targets, prune
  devDependencies and run the runtime image as node instead of root
- bake API_INTERNAL_URL at build time; next start ignores it at runtime
  because rewrite destinations are resolved into routes-manifest.json
- drop CHOKIDAR_USEPOLLING and WATCHPACK_POLLING
- probe /health instead of /, which redirects to /projects and made every
  healthcheck render the project list
- give every service a memory limit and forbid swap in production
- rename the development compose project to leistungsbilanz-dev so its
  down command cannot target the production stack
- bind development ports to localhost
- close the http server and the SQLite handle on SIGTERM/SIGINT
- match probe user agents in the navigation log filter; Node's fetch sends
  one, so the previous check never matched
- exit docker-start.sh when either supervised process dies
- remove drizzle.config.js, a compiled copy drizzle-kit never reads, and the
  pre-Next index.html/styles.css leftovers

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitignore

@@ -1,6 +1,8 @@
 node_modules/
 dist/
 .next/
+# Stray tsc output; drizzle-kit reads drizzle.config.ts.
+/drizzle.config.js
 data/*.db
 data/backups/*.db
 .codex/*.log