Feat v0.6.1-v0.6.2: backup/restore, docs surface, dynamic OpenAPI

v0.6.1 — Backup tooling (.swb ZIP export/import), admin backup section,
docs surface with markdown rendering, 5 reference docs, 6 handler tests.

v0.6.2 — Dark mode contrast fixes, topbar nav, 📖 docs icon, dynamic
OpenAPI spec with extension route merging, docs outline sidebar,
scroll/routing fixes; 7 new tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/static/swagger.html

@@ -256,7 +256,7 @@
   <script src="https://unpkg.com/swagger-ui-dist@5/swagger-ui-bundle.js"></script>
   <script>
     SwaggerUIBundle({
-      url: window.location.pathname.replace(/\/$/, '') + '/openapi.yaml',
+      url: window.location.pathname.replace(/\/$/, '') + '/openapi.json',
       dom_id: '#swagger-ui',
       deepLinking: true,
       presets: [SwaggerUIBundle.presets.apis, SwaggerUIBundle.SwaggerUIStandalonePreset],