feat: add element hover label and refactor to use CSS classes

Add visual feedback for hovered elements:
- Display element selector label (e.g., "p", "h1.title") on hover
- Label positioned at top-left of element with 30% opacity

Refactor all hover/selection styles to use CSS classes instead of inline styles:
- .page-hovered, .page-selected for page states
- .element-hovered, .element-selected for element states
- .element-hover-label for the floating label

This improves maintainability and separation of concerns by moving
styling logic to CSS files instead of JavaScript.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

public/assets/css/pagedjs-interface.css

@@ -144,6 +144,38 @@
   /*--------------------------------------------------------------------------------------*/
 }
 
+/* Hover and selection states for pages and elements */
+.page-hovered {
+  outline: 2px solid #ff8a5050 !important;
+}
+
+.page-selected {
+  outline: 2px solid #ff8a50 !important;
+}
+
+.element-hovered {
+  outline: 2px solid #7136ff50 !important;
+}
+
+.element-selected {
+  outline: 2px dashed #7136ff !important;
+  background-color: #7136ff1a !important;
+}
+
+.element-hover-label {
+  position: absolute;
+  background: #7136ff;
+  color: white;
+  padding: 0.25rem 0.5rem;
+  border-radius: 4px;
+  font-size: 0.875rem;
+  font-weight: 600;
+  opacity: 0.3;
+  pointer-events: none;
+  z-index: 9999;
+  font-family: sans-serif;
+}
+
 /* Marks (to delete when merge in paged.js) */
 
 .pagedjs_marks-crop {