consolidate shop pages into unified LiveView for editor state persistence

Replace individual shop LiveViews with a single Shop.Page that dispatches
to page modules based on live_action. This enables patch navigation between
pages, preserving socket state (including editor state) across transitions.

Changes:
- Add Shop.Page unified LiveView with handle_params dispatch
- Extract page logic into Shop.Pages.* modules (Home, Product, Collection, etc.)
- Update router to use Shop.Page with live_action for all shop routes
- Change navigate= to patch= in shop component links
- Add maybe_sync_editing_blocks to reload editor state when page changes
- Track editor_page_slug to detect cross-page navigation while editing
- Fix picture element height when hover image disabled
- Extract ThemeEditor components for shared use

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/css/admin/components.css

@@ -2534,6 +2534,13 @@
   cursor: pointer;
 }
 
+/* On larger screens, hide the overlay so you can navigate while editing */
+@media (min-width: 768px) {
+  .editor-overlay {
+    display: none;
+  }
+}
+
 /* ── Editor panel ── */
 .editor-panel {
   position: fixed;