fix(web): hygiene — OG image/metadataBase, Header a11y text + nav flag, dead code

- siteConfig.ogImage pointed to an existing asset; metadataBase added so
  relative OG/Twitter URLs resolve against the real origin instead of localhost
- Header sr-only menu label moved to common.json (a11y.openMenu/closeMenu);
  navigation primary styling driven by a NavigationItem.primary flag instead
  of brittle 'Kapcsolat' string comparisons
- remove dead code: lib/site-config.ts (unused hybrid config) and the
  unused, schema-divergent siteConfig.contact.form
- ContactConfig type cleaned up (address/form removed)

Closes MITHOME-77

proto/src/content/common.json

@@ -20,5 +20,9 @@
   "footer": {
     "copyright": "© 2002–{year} mozdIT Bt. Minden jog fenntartva.",
     "address": "Szigetszentmiklós, Magyarország"
+  },
+  "a11y": {
+    "openMenu": "Főmenü megnyitása",
+    "closeMenu": "Főmenü bezárása"
   }
 }

proto/src/content/schema.js

@@ -16,6 +16,7 @@ const schemas = {
     validation: object({ required: string, invalidEmail: string, minLength: string }),
     staging: object({ banner: string }),
     footer: object({ copyright: string, address: string }),
+    a11y: object({ openMenu: string, closeMenu: 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

@@ -197,6 +197,10 @@ export interface CommonContent {
     copyright: string
     address: string
   }
+  a11y: {
+    openMenu: string
+    closeMenu: string
+  }
 }
 
 export interface LegalPageContent {