feat(sprint-5.5): add page preview section with Create button

- New route /pages/preview with empty state ("Создать") and assembled preview
- Preview assembles real site blocks in order (Hero + Doctors ready, rest placeholders)
- localStorage persists created state; "Пересобрать" resets it
- Extracted HeroBlock and DoctorsBlock as reusable components
- Refactored hero and doctors pages to import from components/blocks/
- Sidebar: added "Просмотр страницы" link, bumped to Sprint 5.5 · v0.5.5
- SPRINTS.md: added Sprint 5.5 plan with summary table row

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/components/layout/Sidebar.tsx

@@ -48,6 +48,7 @@ const NAV: NavSection[] = [
   {
     title: "Страницы",
     items: [
+      { label: "Просмотр страницы", href: "/pages/preview" },
       { label: "Главная", href: "/pages/home", soon: true },
       { label: "Заболевание", href: "/pages/disease", soon: true },
       { label: "Все врачи", href: "/pages/doctors", soon: true },
@@ -166,7 +167,7 @@ export function Sidebar() {
           color: "var(--bb-sidebar-text-muted)",
         }}
       >
-        Sprint 5 · v0.5.1
+        Sprint 5.5 · v0.5.5
       </div>
     </aside>
   );