feat: unified preview eye icon component, enhanced search & preview

- Unify filter group and filter value preview icons into shared
  .filter-chip-wrapper + .chip-preview-btn component pattern
- Remove old .toggle-count.clickable inline eye icon approach
- Add dropdown-level event handler for preview buttons (dropdown
  appended to body, needs separate delegation)
- Enhanced EntitySearchEngine with improved product condition
  resolution and preview data
- Add EntityPreviewHandler for richer preview popovers
- Various SCSS improvements for chips, groups, and list-preview

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

sources/scss/components/_groups.scss

@@ -931,6 +931,36 @@
         background-size: 1.25em 1.25em;
     }
 
+    // Single mode — strip padding, borders, backgrounds for clean single-selection UI
+    &[data-mode=single],
+    .mode-single {
+        .groups-container {
+            padding: 0;
+        }
+
+        .group-body {
+            padding: 0;
+        }
+
+        .group-include {
+            padding: 0.5rem;
+            margin-bottom: 0;
+            background: transparent;
+            border: none;
+            border-radius: 0;
+        }
+
+        .selection-group {
+            background: transparent;
+            border: none;
+            margin-bottom: 0;
+        }
+
+        .group-header {
+            display: none;
+        }
+    }
+
     // Condition match count badge
     .condition-match-count {
         display: inline-flex;