feat(project-editor): add field descriptions to General and Branding sections (partial)

Adds a short plain-language description under each field label (new
.field-desc style, section.shared.scss) so a non-developer admin
understands what each field affects, per i18n (en/ru/hy) convention.

Only General and Branding sections are wired up so far - the *Desc i18n
keys for the remaining sections (theme/header/footer/homepage/widgets/
features/languages/navigation) were prepared in translations.ts/en/ru/hy
but not yet wired into their templates. Follow-up work.

src/app/i18n/en.ts

@@ -531,6 +531,107 @@ export const en: Translations = {
     resetSection: 'Reset section',
     confirmResetDraft: 'This discards all unpublished changes and restores the last published configuration. Continue?',
     confirmResetSection: 'This discards unpublished changes in this section only. Continue?',
+    marketplaceNameDesc: 'The name shown to shoppers across the storefront and browser tab.',
+    domainDesc: 'The domain shoppers use to reach this marketplace. Changing it does not move DNS.',
+    descriptionFieldDesc: 'A short summary used for search engines and social link previews.',
+    defaultLanguageDesc: 'The language shown when a shopper has no saved language preference.',
+    supportedLanguagesDesc: 'Comma-separated language codes shoppers can switch to (e.g. en, ru, hy).',
+    logoDesc: 'Full logo image URL, shown in the header on desktop.',
+    smallLogoDesc: 'Compact logo image URL, used where space is limited (e.g. mobile header).',
+    faviconDesc: 'Browser tab icon image URL. Should be a small square image.',
+    marketplaceTitleDesc: 'The page title used by search engines and browser tabs.',
+    primaryColorDesc: 'The main brand color, used on primary buttons and highlights. Must be a valid hex color.',
+    secondaryColorDesc: 'A supporting brand color used for secondary UI elements. Must be a valid hex color.',
+    backgroundColorDesc: 'The default page background color. Must be a valid hex color.',
+    surfaceColorDesc: 'The background color for cards and raised surfaces. Must be a valid hex color.',
+    textColorDesc: 'The default body text color. Must be a valid hex color.',
+    successColorDesc: 'Color used for success messages and positive states. Must be a valid hex color.',
+    warningColorDesc: 'Color used for warning messages and caution states. Must be a valid hex color.',
+    dangerColorDesc: 'Color used for errors and destructive actions. Must be a valid hex color.',
+    themeModeLabel: 'Color mode',
+    themeModeDesc: 'Controls whether the storefront renders in light, dark, or the shopper\'s system preference.',
+    themeModeLight: 'Light',
+    themeModeLightDesc: 'Always use the light color scheme.',
+    themeModeDark: 'Dark',
+    themeModeDarkDesc: 'Always use the dark color scheme.',
+    themeModeSystem: 'System',
+    themeModeSystemDesc: 'Follow the shopper\'s device/browser color scheme preference.',
+    siteLayoutLabel: 'Site layout',
+    siteLayoutDesc: 'The overall page chrome mode used across the storefront.',
+    siteLayoutDefault: 'Default',
+    siteLayoutDefaultDesc: 'Standard layout with a top navigation bar.',
+    siteLayoutSidebarLeft: 'Sidebar (left)',
+    siteLayoutSidebarLeftDesc: 'Adds a left-hand sidebar, typically for category navigation.',
+    siteLayoutCarouselHome: 'Carousel home',
+    siteLayoutCarouselHomeDesc: 'Homepage leads with a full-width carousel/hero.',
+    siteLayoutMinimal: 'Minimal',
+    siteLayoutMinimalDesc: 'Stripped-down chrome with minimal navigation elements.',
+    showLogoDesc: 'Show the marketplace logo in the header.',
+    showSearchDesc: 'Show the search bar in the header.',
+    showCategoriesDesc: 'Show the categories menu entry point in the header.',
+    showLanguagesDesc: 'Show the language switcher in the header.',
+    showCartDesc: 'Show the cart icon/link in the header.',
+    showProfileDesc: 'Show the account/profile entry point in the header.',
+    showWishlistDesc: 'Show the wishlist entry point in the header.',
+    showCompareDesc: 'Show the compare-products entry point in the header.',
+    showRegionDesc: 'Show the region/country selector in the header.',
+    companyNameDesc: 'Legal company name shown in the footer and static pages.',
+    addressDesc: 'Company street address shown in the footer.',
+    phoneDesc: 'Contact phone number shown in the footer.',
+    emailDesc: 'Contact email address shown in the footer.',
+    copyrightDesc: 'Copyright line shown at the bottom of every page.',
+    paymentIconsDesc: 'One payment icon entry per line (image URL and label) shown in the footer.',
+    socialLinksDesc: 'One social link entry per line (platform and URL) shown in the footer.',
+    staticPagesFieldDesc: 'Static pages (about, terms, privacy, etc.) linked from the footer.',
+    sectionVisibleDesc: 'Whether this homepage section is shown to shoppers.',
+    layoutStrategyLabel: 'Layout strategy',
+    layoutStrategyDesc: 'How widgets inside this section are arranged.',
+    layoutStrategyStack: 'Stack',
+    layoutStrategyStackDesc: 'Widgets stack vertically, one after another.',
+    layoutStrategyGrid: 'Grid',
+    layoutStrategyGridDesc: 'Widgets arrange in a multi-column grid.',
+    layoutStrategyHero: 'Hero',
+    layoutStrategyHeroDesc: 'A single large, full-width promotional layout.',
+    layoutStrategyCarousel: 'Carousel',
+    layoutStrategyCarouselDesc: 'Widgets scroll horizontally as a carousel.',
+    layoutStrategySplit: 'Split',
+    layoutStrategySplitDesc: 'Content is split into two side-by-side panes.',
+    sectionColumnsDesc: 'Number of columns to use when the layout strategy supports columns.',
+    widgetLayoutDesc: 'Free-text layout variant name understood by this widget (e.g. "full-bleed", "boxed").',
+    widgetHeightDesc: 'Preferred height for this widget (e.g. "480px" or "60vh").',
+    widgetOverlayDesc: 'Show a dark overlay behind hero text for readability.',
+    widgetAutoplayDesc: 'Automatically rotate hero slides without shopper interaction.',
+    widgetColumnsDesc: 'Number of category tiles per row.',
+    widgetCardsPerRowDesc: 'Number of product cards shown per row.',
+    widgetFiltersDesc: 'Show filter controls alongside the product collection.',
+    widgetShowBadgesDesc: 'Show badges such as "New" or "Sale" on product cards.',
+    widgetShowRatingDesc: 'Show the star rating on product cards.',
+    widgetShowPriceDesc: 'Show the price on product cards.',
+    widgetJsonDesc: 'Raw widget properties as JSON. Used when no dedicated editor exists for this widget type.',
+    wishlistFeatureDesc: 'Let shoppers save products to a wishlist.',
+    compareFeatureDesc: 'Let shoppers compare multiple products side by side.',
+    reviewsFeatureDesc: 'Let shoppers leave and read product reviews.',
+    questionsFeatureDesc: 'Let shoppers ask and read product questions and answers.',
+    commentsFeatureDesc: 'Enable general comments on marketplace content.',
+    recommendationsFeatureDesc: 'Show recommended-product blocks across the storefront.',
+    recentlyViewedFeatureDesc: 'Show a "recently viewed" product list to shoppers.',
+    searchSuggestionsDesc: 'Show live search suggestions as shoppers type.',
+    searchHistoryDesc: 'Remember and show a shopper\'s recent searches.',
+    catalogNavigationModeLabel: 'Catalog navigation mode',
+    catalogNavigationModeDesc: 'How shoppers navigate categories in the catalog.',
+    catalogNavDefault: 'Default',
+    catalogNavDefaultDesc: 'Standard breadcrumb-driven category navigation.',
+    catalogNavLeftCategory: 'Left category navigation',
+    catalogNavLeftCategoryDesc: 'Persistent category tree in a left-hand sidebar.',
+    catalogNavMegaCategory: 'Mega category layout',
+    catalogNavMegaCategoryDesc: 'Expanded dropdown showing subcategories and featured items.',
+    catalogNavTopCarousel: 'Top category carousel',
+    catalogNavTopCarouselDesc: 'Horizontally scrollable category chips above the catalog grid.',
+    newLanguageDesc: 'ISO language code to add as a supported storefront language (e.g. de, fr).',
+    languagesTabDesc: 'Languages available to shoppers. The default language is used as a fallback everywhere.',
+    linkLabelDesc: 'Text shown for this navigation link.',
+    linkUrlDesc: 'Path or URL this navigation link points to.',
+    linkVisibleDesc: 'Whether this navigation link is shown to shoppers.',
   },
   dashboard: {
     title: 'Dashboard',