feat: complete Syndarix rebranding from PragmaStack

- Update PROJECT_NAME to Syndarix in backend config
- Update all frontend components with Syndarix branding
- Replace all GitHub URLs with Gitea Syndarix repo URLs
- Update metadata, headers, footers with new branding
- Update tests to match new URLs
- Update E2E tests for new repo references
- Preserve "Built on PragmaStack" attribution in docs

Closes #13

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/app/[locale]/page.tsx

@@ -1,7 +1,7 @@
 /* istanbul ignore file -- @preserve Landing page with complex interactions tested via E2E */
 /**
  * Homepage / Landing Page
- * Main landing page for the PragmaStack project
+ * Main landing page for the Syndarix project
  * Showcases features, tech stack, and provides demos for developers
  */
 
@@ -68,7 +68,7 @@ export default function Home() {
         <div className="container mx-auto px-6 py-8">
           <div className="flex flex-col md:flex-row items-center justify-between gap-4">
             <div className="text-sm text-muted-foreground">
-              © {new Date().getFullYear()} PragmaStack. MIT Licensed.
+              © {new Date().getFullYear()} Syndarix. MIT Licensed.
             </div>
             <div className="flex items-center gap-6 text-sm text-muted-foreground">
               <Link href="/demos" className="hover:text-foreground transition-colors">