feat(cms): ContactSubmissions Payload collection (MITHOME-94)

/api/contact used to write straight to a raw, Payload-external MongoDB
collection (contact_submissions, via proto/src/lib/mongodb.ts's
getCollection) — the client had no way to see incoming messages except
by reading the database directly. Rate limiting, length caps, email
validation, and spam-keyword filtering all stay on the route exactly
as before; only the persistence target changed.

New: src/collections/ContactSubmissions.ts (name, email, subject,
message, gdprConsent checkbox, status select defaulting to "new").
Deliberately no custom `access` block — Payload's default
(authenticated-only for every REST operation) is exactly right here:
the client reads submissions in the admin, nobody can read or write
them through the public REST API, and the route's own write uses the
Local API (payload.create), which runs with overrideAccess: true by
default and so isn't blocked by that same rule. No versions/drafts
(a submission is a fact, not editable content) and no field-level
length/format validation duplicated in the collection, matching the
ticket's explicit scope: those checks live on the route.

route.ts: replaced getCollection()/insertOne() with
getPayload({config}).create({ collection: 'contact-submissions', ... }).
Removed the now-unused getCollection() helper from lib/mongodb.ts
(checkMongoConnection/getDb stay, used by /api/health) and its test.

Test gotcha worth documenting: next/jest's SWC transform rewrites the
`@payload-config` tsconfig-path alias to a real relative specifier at
transform time, so `jest.mock('@payload-config', ...)` never actually
intercepts what route.ts requires — it silently falls through to the
real payload.config.ts (mongooseAdapter, live Mongo needed). Fixed by
mocking the resolved relative path instead
(`jest.mock('../../../payload.config', ...)`); documented inline in
route.unit.test.ts for whoever hits this next (MITHOME-96 will need
the same trick for other Payload-backed routes/collections).

Verified live end-to-end, not just the test suite: submitted the real
contact form on /hu/kapcsolat, got the success message, found the
submission in /admin/collections/contact-submissions with all fields
correct (including gdprConsent checked and status "Új"/New), then
deleted the test record. Zero console errors in a fresh tab. Gate:
tsc, lint, unit tests (50 passed — one fewer than before, the removed
getCollection test), production build all green.

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

proto/src/payload.config.ts

@@ -17,6 +17,10 @@
  * MITHOME-120: admin gyorskeresés (QuickSearch) az admin.components.header
  * slotba regisztrálva — teljes szöveges keresés minden Global/Collection
  * mezőjében, mindkét locale-ban.
+ * MITHOME-94: ContactSubmissions collection — a /api/contact korábban egy
+ * nyers, Payload-on kívüli Mongo collection-be (`contact_submissions`,
+ * proto/src/lib/mongodb.ts) írt, amit az ügyfél nem látott sehol az admin
+ * felületen. Mostantól Payload collection, a route.ts a Local API-n ír bele.
  */
 import path from 'path'
 import { fileURLToPath } from 'url'
@@ -29,6 +33,7 @@ import { Users } from './collections/Users'
 import { LegalPages } from './collections/LegalPages'
 import { Media } from './collections/Media'
 import { Partners } from './collections/Partners'
+import { ContactSubmissions } from './collections/ContactSubmissions'
 import { Home } from './globals/Home'
 import { About } from './globals/About'
 import { Services } from './globals/Services'
@@ -55,7 +60,7 @@ export default buildConfig({
 
   editor: lexicalEditor(),
 
-  collections: [Users, LegalPages, Media, Partners],
+  collections: [Users, LegalPages, Media, Partners, ContactSubmissions],
 
   globals: [Home, About, Services, Contact, Common],