feat(project-editor): finish field descriptions + enum dropdowns across all sections

Wires up the remaining editor sections (theme, header, footer, homepage,
widgets, features, languages, navigation) with the description text and
dropdown UX started for General/Branding:

- Every enum-backed field is now a <select> with a description per option,
  not free text: theme.mode, the new site-wide layout.type (previously had
  no editor at all - added to the Theme section, and added to that
  section's reset-scope), homepage section layout.strategy, and
  catalog.navigationMode (also previously unedited, added to Features).
- Every other field (colors, header toggles, footer contact/company fields,
  widget props, feature flags, language add, nav link label/url/visible)
  gets a one-line plain-language description under its label via the new
  *Desc i18n keys (en/ru/hy) prepared earlier.
- Genuinely open text (widget layout variant strings, JSON props) stays
  free text, description-only, per the existing widgetLayoutDesc/widgetJsonDesc
  wording - not force-fit into a dropdown.

Verified: tsc --noEmit and ng build both clean.

src/app/features/project-editor/sections/theme-section.component.ts

@@ -2,7 +2,19 @@ import { ChangeDetectionStrategy, Component, inject } from '@angular/core';
 import { FormsModule } from '@angular/forms';
 import { ProjectEditorFacade } from '../facade/project-editor.facade';
 import { TranslatePipe } from '../../../i18n/translate.pipe';
-import { ThemePaletteConfig } from '../../../shared/models/config';
+import { PlatformLayoutType, ThemePaletteConfig } from '../../../shared/models/config';
+
+export interface ThemeModeOption {
+  value: 'light' | 'dark' | 'system';
+  labelKey: string;
+  descKey: string;
+}
+
+export interface SiteLayoutOption {
+  value: PlatformLayoutType;
+  labelKey: string;
+  descKey: string;
+}
 
 @Component({
   selector: 'app-project-editor-theme-section',
@@ -16,10 +28,45 @@ export class ProjectEditorThemeSectionComponent {
   private readonly facade = inject(ProjectEditorFacade);
   readonly bootstrap = this.facade.bootstrap;
 
+  readonly themeModeOptions: ThemeModeOption[] = [
+    { value: 'light', labelKey: 'builder.themeModeLight', descKey: 'builder.themeModeLightDesc' },
+    { value: 'dark', labelKey: 'builder.themeModeDark', descKey: 'builder.themeModeDarkDesc' },
+    { value: 'system', labelKey: 'builder.themeModeSystem', descKey: 'builder.themeModeSystemDesc' },
+  ];
+
+  readonly siteLayoutOptions: SiteLayoutOption[] = [
+    { value: 'default', labelKey: 'builder.siteLayoutDefault', descKey: 'builder.siteLayoutDefaultDesc' },
+    { value: 'sidebar-left', labelKey: 'builder.siteLayoutSidebarLeft', descKey: 'builder.siteLayoutSidebarLeftDesc' },
+    { value: 'carousel-home', labelKey: 'builder.siteLayoutCarouselHome', descKey: 'builder.siteLayoutCarouselHomeDesc' },
+    { value: 'minimal', labelKey: 'builder.siteLayoutMinimal', descKey: 'builder.siteLayoutMinimalDesc' },
+  ];
+
   updatePalette<K extends keyof ThemePaletteConfig>(key: K, value: string): void {
     this.facade.updateBootstrap(current => ({
       ...current,
       theme: { ...current.theme, palette: { ...current.theme.palette, [key]: value } }
     }));
   }
+
+  updateThemeMode(mode: string): void {
+    this.facade.updateBootstrap(current => ({
+      ...current,
+      theme: { ...current.theme, mode: mode as 'light' | 'dark' | 'system' }
+    }));
+  }
+
+  updateSiteLayout(type: string): void {
+    this.facade.updateBootstrap(current => ({
+      ...current,
+      layout: { ...current.layout, type: type as PlatformLayoutType }
+    }));
+  }
+
+  themeModeDescKey(mode: string): string {
+    return this.themeModeOptions.find(option => option.value === mode)?.descKey ?? '';
+  }
+
+  siteLayoutDescKey(type: string): string {
+    return this.siteLayoutOptions.find(option => option.value === type)?.descKey ?? '';
+  }
 }