feat(builder): implement reusable media library

Media dashboard (real total/images/SVG/logos/unused/storage/alt-coverage, computed from actual assets + a bootstrap usage scan, no fabricated stats); gallery gets grid/list toggle, type filter, sort, drag-and-drop + multi-file upload with cancel/retry and friendly error mapping, lazy thumbnails, multi-select with bulk delete/download/export-metadata; asset details drawer shows real dimensions/size/format/date/usage locations (walks bootstrap config for exact URL matches, reports not-used rather than guessing) plus editable alt text/caption/description/decorative flag with missing-alt warning; shared MediaPickerComponent (already the one reusable picker used by content management) gains type filter, a recent shortcut, and keyboard grid navigation.

src/app/i18n/translations.ts

@@ -1150,6 +1150,71 @@ export interface Translations {
     confirm: string;
     emptyTitle: string;
     emptyDescription: string;
+    allFolders: string;
+    newFolder: string;
+    editTags: string;
+    totalAssets: string;
+    logos: string;
+    unused: string;
+    storageUsed: string;
+    altCoverage: string;
+    allTypes: string;
+    typeImage: string;
+    typeSvg: string;
+    typePdf: string;
+    sortRecent: string;
+    sortName: string;
+    sortSize: string;
+    viewMode: string;
+    viewGrid: string;
+    viewList: string;
+    dropHint: string;
+    cancelUpload: string;
+    retry: string;
+    errorTooLarge: string;
+    errorUnsupportedType: string;
+    errorGeneric: string;
+    selectedCount: string;
+    download: string;
+    exportMetadata: string;
+    bulkDelete: string;
+    bulkDeleteConfirm: string;
+    clearSelection: string;
+    guideCopy: string;
+    missingAlt: string;
+    usageCount: string;
+    detailsTitle: string;
+    filename: string;
+    format: string;
+    fileSize: string;
+    dimensions: string;
+    uploadDate: string;
+    lastUsed: string;
+    usageCountLabel: string;
+    usedIn: string;
+    notUsed: string;
+    unknownValue: string;
+    altText: string;
+    altTextHelp: string;
+    decorative: string;
+    missingAltWarning: string;
+    caption: string;
+    description: string;
+    usage: {
+      brand: string;
+      theme: string;
+      header: string;
+      footer: string;
+      staticPage: string;
+      homepage: string;
+      catalog: string;
+      productPage: string;
+      widget: string;
+      company: string;
+      seo: string;
+      navigation: string;
+      other: string;
+    };
   };
   // Sprint 28: only the new empty-state copy this sprint's skeleton/empty-
   // state consistency fix introduces - NOT the full adminProducts/