Set functions runtime to Node 22 (max firebase-tools supports)

engines.node=24 breaks firebase-tools at function load time — both the
emulator and deploy reject it:

  FirebaseError: Detected node engine 24 in package.json, which is not a
  supported version. Valid versions are 20, 22

This surfaced as an e2e failure: the functions emulator refused to load,
so vote aggregation never ran and feedback/talk.spec.js timed out.

nodejs24 is GA on Cloud Functions, but no released firebase-tools
(latest 15.20.0) supports it yet, so 22 is the highest usable runtime.
Revisit 24 once firebase-tools ships nodejs24 support.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: HugoGresse

functions/package.json

@@ -13,7 +13,7 @@
         "test": "vitest"
     },
     "engines": {
-        "node": "24"
+        "node": "22"
     },
     "main": "lib/index.js",
     "dependencies": {