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/en.ts

@@ -1152,6 +1152,71 @@ export const en: Translations = {
     confirm: 'Delete',
     emptyTitle: 'No files yet',
     emptyDescription: 'Upload an image or document to get started.',
+    allFolders: 'All folders',
+    newFolder: 'New folder',
+    editTags: 'Edit tags',
+    totalAssets: 'Total assets',
+    logos: 'Logos',
+    unused: 'Unused',
+    storageUsed: 'Storage used',
+    altCoverage: 'Alt text coverage',
+    allTypes: 'All types',
+    typeImage: 'Images',
+    typeSvg: 'SVG',
+    typePdf: 'PDF',
+    sortRecent: 'Recent',
+    sortName: 'Name',
+    sortSize: 'Size',
+    viewMode: 'View',
+    viewGrid: 'Grid',
+    viewList: 'List',
+    dropHint: 'Drag and drop images here, or use Upload above.',
+    cancelUpload: 'Cancel',
+    retry: 'Retry',
+    errorTooLarge: 'That file is too large. Try a smaller file.',
+    errorUnsupportedType: 'That file type is not supported. Use JPG, PNG, WebP, GIF, SVG, or PDF.',
+    errorGeneric: 'Upload failed. Please try again.',
+    selectedCount: 'selected',
+    download: 'Download',
+    exportMetadata: 'Export metadata',
+    bulkDelete: 'Delete selected',
+    bulkDeleteConfirm: 'Delete the selected files? This cannot be undone.',
+    clearSelection: 'Clear selection',
+    guideCopy: 'Reusing an existing asset avoids duplicate uploads and keeps your storage tidy. For best results upload images around 1200×1200px for hero/banner use and compress large photos before uploading.',
+    missingAlt: 'Missing alt text',
+    usageCount: 'uses',
+    detailsTitle: 'Asset details',
+    filename: 'Filename',
+    format: 'Format',
+    fileSize: 'File size',
+    dimensions: 'Dimensions',
+    uploadDate: 'Uploaded',
+    lastUsed: 'Last used',
+    usageCountLabel: 'Usage count',
+    usedIn: 'Used in',
+    notUsed: 'Not currently used anywhere.',
+    unknownValue: 'Unknown',
+    altText: 'Alt text',
+    altTextHelp: 'Describes the image for screen readers and search engines.',
+    decorative: 'Decorative (no alt text needed)',
+    missingAltWarning: 'This image has no alt text and is not marked decorative — screen reader users won’t know what it shows.',
+    caption: 'Caption',
+    description: 'Description',
+    usage: {
+      brand: 'Logo',
+      theme: 'Theme',
+      header: 'Header',
+      footer: 'Footer',
+      staticPage: 'Static page',
+      homepage: 'Homepage',
+      catalog: 'Catalog',
+      productPage: 'Product page',
+      widget: 'Widget',
+      company: 'Company info',
+      seo: 'SEO',
+      navigation: 'Navigation',
+      other: 'Other',
+    },
   },
   adminCategories: {
     chooseImage: 'Choose image',