chore(node): build for the runtime the image carries

`engines`, `@types/node` and the three esbuild targets said node20 while both
stages of the image have been node:24-alpine for a while — and since
24.10.2026 the development machines run 24 too. So the bundles are built for
exactly the runtime that carries them instead of for a version nobody runs
any more.

`npm run check`: 110 files, 1825 tests, green on node 24.22.1.

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

packages/server/package.json

@@ -8,7 +8,7 @@
     ".": "./src/index.ts"
   },
   "scripts": {
-    "build": "esbuild src/main.ts src/simWorker.ts src/precompressMain.ts --bundle --platform=node --format=esm --target=node20 --outdir=dist --out-extension:.js=.mjs --external:pg-native --banner:js=\"import { createRequire as createBundleRequire } from 'node:module'; const require = createBundleRequire(import.meta.url);\"",
+    "build": "esbuild src/main.ts src/simWorker.ts src/precompressMain.ts --bundle --platform=node --format=esm --target=node24 --outdir=dist --out-extension:.js=.mjs --external:pg-native --banner:js=\"import { createRequire as createBundleRequire } from 'node:module'; const require = createBundleRequire(import.meta.url);\"",
     "start": "node dist/main.mjs"
   },
   "dependencies": {