feat(cms): Home/About/Services/Contact/Common Globals + JSON migration (MITHOME-87)

Payload Global configs mirroring proto/src/content/types.ts:
- src/globals/{Home,About,Services,Contact,Common}.ts
- src/globals/fields/stringArray.ts — shared helper: Payload has no
  native string[] field, so every plain string array from the old
  content types (trustBullets, paragraphs, features, spec items, …)
  becomes an array of one-field { value } objects.
- home.partners is intentionally NOT included — that becomes its own
  Partners collection (logo -> Media upload) in MITHOME-89, to avoid
  two disagreeing sources for the same data.
- contact.form.fields.gdpr.label stays a plain textarea (not lexical
  richText): the JSON source is a hand-written HTML string with an
  <a> tag; richText's node-tree serialization would need its own
  migration/render logic, out of scope for this bootstrap pass.

scripts/migrate-content-to-payload.ts: one-shot, idempotent Local API
migration reading the existing JSON files and calling updateGlobal —
does not touch or delete the JSON files. Run via the new
`npm run migrate:content` script.

Registered the five Globals in payload.config.ts.

Also included here (belongs with the previous "resolve double-root-
layout conflict" commit but didn't actually get staged there —
verified only now by diffing HEAD against the working tree):
(frontend)/layout.tsx's relative imports corrected to ../../ instead
of ../ (one directory deeper than the original src/app/layout.tsx).

Verified:
- npm run build / lint, tsc --noEmit, npm test (58 passed) all clean
- npm run migrate:content against the real dev MongoDB container,
  then read back via payload.findGlobal() — hero.title, trustBullets,
  services.items[0].features, footer.address, faq.items.length all
  match the JSON source
- Real browser: logged into /admin, opened the Home global editor —
  Hero/Trust bullets group renders and shows the migrated Hungarian
  content correctly (see screenshot shared in chat)

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

proto/src/globals/Common.ts

@@ -0,0 +1,73 @@
+import type { GlobalConfig } from 'payload'
+
+/** Mirrors CommonContent (proto/src/content/types.ts) — MITHOME-87. */
+export const Common: GlobalConfig = {
+  slug: 'common',
+  admin: {
+    group: 'Oldalak',
+  },
+  fields: [
+    {
+      name: 'buttons',
+      type: 'group',
+      fields: [
+        { name: 'contact', type: 'text', required: true },
+        { name: 'learnMore', type: 'text', required: true },
+        { name: 'webmail', type: 'text', required: true },
+        { name: 'sendMessage', type: 'text', required: true },
+      ],
+    },
+    {
+      name: 'labels',
+      type: 'group',
+      fields: [
+        { name: 'required', type: 'text', required: true },
+        { name: 'features', type: 'text', required: true },
+      ],
+    },
+    {
+      name: 'validation',
+      type: 'group',
+      fields: [
+        { name: 'required', type: 'text', required: true },
+        { name: 'invalidEmail', type: 'text', required: true },
+        {
+          name: 'minLength',
+          type: 'text',
+          required: true,
+          admin: {
+            description: 'A {min} placeholder futásidőben cserélődik ki.',
+          },
+        },
+      ],
+    },
+    {
+      name: 'staging',
+      type: 'group',
+      fields: [{ name: 'banner', type: 'text', required: true }],
+    },
+    {
+      name: 'footer',
+      type: 'group',
+      fields: [
+        {
+          name: 'copyright',
+          type: 'text',
+          required: true,
+          admin: {
+            description: 'A {year} placeholder futásidőben cserélődik ki.',
+          },
+        },
+        { name: 'address', type: 'text', required: true },
+      ],
+    },
+    {
+      name: 'a11y',
+      type: 'group',
+      fields: [
+        { name: 'openMenu', type: 'text', required: true },
+        { name: 'closeMenu', type: 'text', required: true },
+      ],
+    },
+  ],
+}