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/components/Footer.tsx

@@ -131,11 +131,12 @@ export default function Footer() {
           style={{ borderColor: 'var(--color-border)' }}
         >
           <div className="flex flex-col sm:flex-row justify-between items-center gap-4">
-            <p 
+            <p
               className="text-sm"
               style={{ color: 'var(--color-foreground-muted)' }}
             >
-              {siteConfig.footer.copyright}
+              {/* Copyright text is CMS-editable (common.json); {year} resolves to the current year */}
+              {content.common.footer.copyright.replace('{year}', String(new Date().getFullYear()))}
             </p>
             <div className="flex items-center gap-6">
               {siteConfig.footer.links.map((link) => (