Address Copilot review feedback on #2091

- Pin pnpm to the exact version (10.10.0) when installing it in the
  production Dockerfile, matching packageManager and Dockerfile.e2e,
  instead of a floating major that can drift the lockfile behaviour.
- Fix mockEndpoint's array header handling in the api test utility:
  append each value instead of joining with a comma, which is how
  multi-value headers (e.g. set-cookie) are actually represented.
- Update apps/remark42's engines to node >=18 / pnpm >=10, matching
  the pnpm 10 requirement instead of the stale node 16 / pnpm 8 range.

Dockerfile

@@ -11,7 +11,7 @@ COPY ./frontend/apps/remark42/package.json /srv/frontend/apps/remark42/
 RUN \
   if [[ -z "$SKIP_FRONTEND_BUILD" || -z "$SKIP_FRONTEND_TEST" ]]; then \
     apk add --no-cache --update git && \
-    npm i -g pnpm@10; \
+    npm i -g pnpm@10.10.0; \
   fi
 
 RUN --mount=type=cache,id=pnpm,target=/root/.pnpm-store/v3 \

frontend/apps/remark42/package.json

@@ -22,8 +22,8 @@
     "translation:check": "node ./tasks/checkTranslation.js"
   },
   "engines": {
-    "node": ">=16.15",
-    "pnpm": ">=8"
+    "node": ">=18",
+    "pnpm": ">=10"
   },
   "packageManager": "pnpm@10.10.0",
   "dependencies": {

frontend/packages/api/tests/test-utils.ts

@@ -41,7 +41,11 @@ export function mockEndpoint(
 			const responseHeaders = new Headers()
 			if (headers) {
 				for (const [key, value] of Object.entries(headers)) {
-					responseHeaders.set(key, Array.isArray(value) ? value.join(', ') : value)
+					if (Array.isArray(value)) {
+						for (const v of value) responseHeaders.append(key, v)
+					} else {
+						responseHeaders.set(key, value)
+					}
 				}
 			}