feat(cms): Partners + Media collection MVP (MITHOME-89)

Payload built-in upload collection (Media) + a Partners collection
(name, url, logo -> Media relationship) mirroring home.json's
partners.items.

Scope decision (see Plane MITHOME-89/118): the old logo editor
(crop/rotate/transparent-background — MITHOME-76/84) is entirely
client-side canvas logic (scripts/cms-logo-client.js, 345 lines), not
server-side processing. Porting that UX into the Payload admin is a
real custom React field component, split into its own ticket
(MITHOME-118) rather than bundled here. This ticket covers plain
upload only.

- src/collections/Media.ts, src/collections/Partners.ts, registered
  in payload.config.ts.
- migrate-content-to-payload.ts: upsertPartner() uploads the existing
  processed logo file (filePath) into Media (idempotent — matched by
  `alt` == partner name) and upserts the Partner document (matched by
  `name`).
- .gitignore: Payload's default local upload storage lands at
  proto/media/ (not proto/public/) — runtime data, not source, needs
  a persistent volume in staging/production (flagged for MITHOME-97).
  Also ignored the generated src/payload-types.ts.

Verified: migration run twice against the real dev MongoDB produced
exactly 1 Media doc + 1 Partner doc (no duplicates, confirmed via
mongosh) with the correct file size (12289 bytes, matching the source
PNG). Real browser: logged into /admin, Partners list shows the
migrated entry, and the document editor renders the logo thumbnail
(270x80, 12KB) correctly. build/lint/tsc/test (58 passed) all clean.

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

proto/src/payload.config.ts

@@ -8,7 +8,9 @@
  * MITHOME-87: Home/About/Services/Contact/Common Globals hozzáadva — ezek
  * tükrözik a proto/src/content/pages/*.json + common.json struktúráját.
  * MITHOME-88: LegalPages collection hozzáadva (adatvedelem, hasznalati-
- * feltetelek). A Partners/Media collectionök a MITHOME-89-ben kerülnek be.
+ * feltetelek).
+ * MITHOME-89: Partners + Media collection (MVP — feltöltés, a vágás/
+ * áttetszővé tétel szerkesztő külön, MITHOME-118).
  */
 import path from 'path'
 import { fileURLToPath } from 'url'
@@ -19,6 +21,8 @@ import sharp from 'sharp'
 
 import { Users } from './collections/Users'
 import { LegalPages } from './collections/LegalPages'
+import { Media } from './collections/Media'
+import { Partners } from './collections/Partners'
 import { Home } from './globals/Home'
 import { About } from './globals/About'
 import { Services } from './globals/Services'
@@ -37,7 +41,7 @@ export default buildConfig({
 
   editor: lexicalEditor(),
 
-  collections: [Users, LegalPages],
+  collections: [Users, LegalPages, Media, Partners],
 
   globals: [Home, About, Services, Contact, Common],