Dockerfile: copy moments.js; guard test for required top-level modules

The 5497e8b image lacked moments.js, so the reader crashed at start on
docker-01. test/dockerfile.test.js follows server.js requires and fails
when a top-level module is not copied into the image.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/dockerfile.test.js

@@ -0,0 +1,22 @@
+'use strict';
+// The image copies top-level modules by name; a new module missing there crashes the reader at start.
+const test = require('node:test'), assert = require('node:assert/strict');
+const fs = require('fs'), path = require('path');
+const root = path.resolve(__dirname, '..');
+
+test('every top-level module the reader requires is copied into the image', () => {
+  const dockerfile = fs.readFileSync(path.join(root, 'Dockerfile'), 'utf8');
+  const copied = new Set(dockerfile.split('\n').filter(line => line.startsWith('COPY ')).flatMap(line => line.split(/\s+/).slice(1, -1)));
+  const pending = ['server.js'], seen = new Set();
+  while (pending.length) {
+    const file = pending.pop();
+    if (seen.has(file)) continue;
+    seen.add(file);
+    for (const [, name] of fs.readFileSync(path.join(root, file), 'utf8').matchAll(/require\('\.\/([\w.-]+?)(?:\.js)?'\)/g)) {
+      // A folder (e.g. ./greatest) is copied as a whole; only single files need their own name in COPY.
+      if (fs.existsSync(path.join(root, name)) && fs.statSync(path.join(root, name)).isDirectory()) assert.ok(copied.has(name), `${name}/ is not copied`);
+      else pending.push(name + '.js');
+    }
+  }
+  for (const file of seen) assert.ok(copied.has(file), `${file} is required but not copied by the Dockerfile`);
+});