refactor: move navigation page from /components to /blocks section

- Moved /components/navigation → /blocks/navigation
- Updated Sidebar: navigation is now first item in "Блоки"
- Updated PreviewClient block path
- Updated seed block path
- Updated SPRINTS.md

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

apps/api/prisma/seed.ts

@@ -7,7 +7,7 @@ const prisma = new PrismaClient({ adapter });
 
 const BLOCKS = [
   {
-    path: '/components/navigation',
+    path: '/blocks/navigation',
     name: 'Шапка / Навигация',
     version: 'v1.0',
     isInPreview: true,