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/docs/design-system/00-quick-start.md

@@ -1,6 +1,6 @@
 # Quick Start Guide
 
-Get up and running with the PragmaStack design system immediately. This guide covers the essential patterns you need to build 80% of interfaces.
+Get up and running with the Syndarix design system immediately. This guide covers the essential patterns you need to build 80% of interfaces.
 
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