feat(categories): implement professional category management experience

Categories dashboard (real total/visible/hidden/empty/root/subcategory/missing-image/missing-SEO/last-modified/completion% stats, recommended next action); tree view is now a real expand/collapse hierarchy (state persisted via LocalStorageService) with keyboard navigation (arrow keys, jump-to-parent), search that force-expands and keeps only matching branches + their ancestors/descendants instead of silently dropping deep matches; added Table/Cards views alongside the tree with density and saved column visibility; real bulk actions (show/hide/delete/assign parent/assign image via the Media Library picker/duplicate via the existing createCategory call/CSV export) plus the pre-existing single-item actions; reusable CategoryHealthWidget (image/SEO/description/valid-parent/visibility/products-assigned + completion%); editor reorganized into General/Media/SEO/Visibility/Navigation/Attributes/Advanced tabs, media now uses the shared ImageFieldComponent, SEO explains fields in plain language with a live preview, Navigation tab shows real breadcrumb/children/visibility-based nav status, Attributes uses the shared KeyValueEditorComponent. Filled in the adminCategories i18n namespace (previously only 2 of ~90 referenced keys existed) across en/ru/hy. Also fixed the pre-existing bug where a filtered/searched category list could silently drop a matched descendant whose ancestor's title didn't match, by loading the full catalog once and filtering client-side.

src/app/i18n/en.ts

@@ -1221,6 +1221,84 @@ export const en: Translations = {
   adminCategories: {
     chooseImage: 'Choose image',
     replaceImage: 'Replace image',
+    search: 'Search categories…',
+    showDeleted: 'Show deleted',
+    create: 'Create category',
+    edit: 'Edit category',
+    title: 'Title',
+    slug: 'URL slug',
+    slugTaken: 'This slug is already used by another category.',
+    parent: 'Parent category',
+    noParent: 'No parent (top level)',
+    icon: 'Icon',
+    image: 'Image',
+    imageHint: 'Shown in category listings and navigation.',
+    description: 'Description',
+    items: 'products',
+    status: { draft: 'Draft', published: 'Published' },
+    restore: 'Restore',
+    saveDraft: 'Save draft',
+    publish: 'Publish',
+    confirmDelete: 'Delete this category? This cannot be undone.',
+    confirmLeaveUnsaved: 'You have unsaved changes. Leave without saving?',
+    deleteBlocked: 'This category can\'t be deleted while it has subcategories or assigned products.',
+    emptyTitle: 'No categories yet',
+    emptyDescription: 'Create your first category to start organizing products.',
+    emptyGuide: 'Categories help customers browse and find products. Start with a few broad top-level categories (e.g. Clothing, Electronics), then add subcategories as your catalog grows — avoid nesting more than 2-3 levels deep.',
+    viewTree: 'Tree',
+    viewCards: 'Cards',
+    expandAll: 'Expand all',
+    collapseAll: 'Collapse all',
+    expandNode: 'Expand',
+    collapseNode: 'Collapse',
+    jumpToParent: 'Jump to parent',
+    deletedBadge: 'Deleted',
+    column_slug: 'Slug',
+    column_items: 'Products',
+    column_status: 'Status',
+    column_visibility: 'Visibility',
+    column_updated: 'Last updated',
+    bulkAssignParent: 'Assign parent',
+    bulkAssignImage: 'Assign image',
+    groupGeneral: 'General',
+    groupMedia: 'Media',
+    groupSeo: 'SEO',
+    groupVisibility: 'Visibility',
+    groupNavigation: 'Navigation',
+    groupAttributes: 'Attributes',
+    groupAdvanced: 'Advanced',
+    visibilityExplain: 'A hidden category and its products stay out of the storefront navigation and search until you make it visible again.',
+    navBreadcrumb: 'Breadcrumb',
+    navRoot: 'This is a top-level category.',
+    navChildren: 'Subcategories',
+    navNoChildren: 'No subcategories yet.',
+    navAppearsIn: 'Where this appears',
+    navAppearsVisible: 'Visible in catalog navigation and search.',
+    navAppearsHidden: 'Hidden — not shown in catalog navigation while hidden.',
+    itemsCountLabel: 'Assigned products',
+    createdAtLabel: 'Created',
+    healthImage: 'Image',
+    healthSeo: 'SEO',
+    healthDescription: 'Description',
+    healthParent: 'Parent',
+    healthVisibility: 'Visibility',
+    healthProducts: 'Products assigned',
+    totalCategories: 'Total categories',
+    visibleCount: 'Visible',
+    hiddenCount: 'Hidden',
+    emptyCount: 'Empty',
+    rootCount: 'Root categories',
+    subCount: 'Subcategories',
+    missingImagesCount: 'Missing images',
+    missingSeoCount: 'Missing SEO',
+    lastModified: 'Last modified',
+    lastModifiedNever: 'Never',
+    completionLabel: 'Completion',
+    recommendedNext: 'Recommended next step',
+    recommendAddImage: 'A category has no image — add one so it looks trustworthy in listings.',
+    recommendAddSeo: 'A category is missing a search title or description — add one so it can be found.',
+    recommendFillEmpty: 'A category has no products assigned — add products or consider hiding it.',
+    recommendNone: 'Nice work — your category structure is in good shape.',
   },
   adminProducts: {
     emptyTitle: 'No products found',