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/components/dev/DevLayout.tsx

@@ -96,12 +96,12 @@ export function DevLayout({ children }: DevLayoutProps) {
             <div className="flex items-center gap-3 shrink-0">
               <Image
                 src="/logo-icon.svg"
-                alt="PragmaStack Logo"
+                alt="Syndarix Logo"
                 width={24}
                 height={24}
                 className="h-6 w-6"
               />
-              <h1 className="text-base font-semibold">PragmaStack</h1>
+              <h1 className="text-base font-semibold">Syndarix</h1>
               <Badge variant="secondary" className="text-xs">
                 Dev
               </Badge>