feat(footer): CMS-editable copyright with 2002–current year range

The copyright text lived in site.ts with a build-time year and was not
CMS-editable. It now lives in common.json (footer.copyright, editable via
the Közös szövegek tab) with a {year} placeholder that resolves to the
current year at render: '© 2002–{year} mozdIT Bt. Minden jog fenntartva.'
Schema and types extended; site.ts keeps only the footer links.

Closes MITHOME-66

proto/src/content/common.json

@@ -16,5 +16,8 @@
   },
   "staging": {
     "banner": "⚠ STAGING / TESZTKÖRNYEZET — A STAGING OLDALT LÁTOD"
+  },
+  "footer": {
+    "copyright": "© 2002–{year} mozdIT Bt. Minden jog fenntartva."
   }
 }

proto/src/content/schema.js

@@ -15,6 +15,7 @@ const schemas = {
     labels: object({ required: string, features: string }),
     validation: object({ required: string, invalidEmail: string, minLength: string }),
     staging: object({ banner: string }),
+    footer: object({ copyright: string }),
   }),
   home: object({
     hero: object({ title: string, subtitle: string, description: string, trustBullets: array(string), cta: object({ primary: ctaLink, secondary: ctaLink }) }),

proto/src/content/types.ts

@@ -193,6 +193,9 @@ export interface CommonContent {
   staging: {
     banner: string
   }
+  footer: {
+    copyright: string
+  }
 }
 
 export interface LegalPageContent {