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

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

frontend/src/components/layout/Header.tsx

@@ -86,12 +86,12 @@ export function Header() {
           <Link href="/" className="flex items-center space-x-2">
             <Image
               src="/logo-icon.svg"
-              alt="PragmaStack Logo"
+              alt="Syndarix Logo"
               width={32}
               height={32}
               className="h-8 w-8"
             />
-            <span className="text-xl font-bold text-foreground">PragmaStack</span>
+            <span className="text-xl font-bold text-foreground">Syndarix</span>
           </Link>
 
           {/* Navigation Links */}