fix(builder): composition audit fixes for project editor sections

- Reset-section button: raw <button> with hardcoded colors -> app-button variant="danger"
- section.shared.scss: raw button/input/select colors switched to CSS theme vars (--primary-color, --bg-primary, --bg-secondary, --error-color) instead of bare hex
- save-bar scss referenced nonexistent CSS vars (--surface, --border, --warning, --danger, --muted-foreground, --info-bg, --info) that always fell back to hardcoded hex; renamed to the real theme vars (--bg-primary, --border-color, --warning-color, --error-color, --text-secondary, --info-color) so the save bar is actually theme-aware
- footer/homepage/widgets section scss: nonexistent --danger-color var renamed to --error-color
- static-pages-editor: replaced dead `.editor-section-card` wrapper class (removed from shared stylesheet in the Sprint 30 redesign, never migrated here) with app-section-card, restoring the card chrome every sibling editor section has
- widgets-section: empty state (no widgets) rendered nothing; added app-empty-state
- homepage-section: empty state (no homepage page) rendered nothing; added app-empty-state
- navigation-section: header/footer nav move-up/move-down buttons had no accessible name (bare uarr/darr glyphs); added aria-label
- Added builder.widgetsEmptyTitle/Desc and builder.homepageEmptyTitle/Desc i18n keys (en/ru/hy)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/features/content-management/components/static-pages-editor.component.html

@@ -1,4 +1,4 @@
-<section class="editor-section-card">
+<app-section-card>
   @if (fieldError('staticPages'); as msg) {
     <p class="editor-error">{{ msg }}</p>
   }
@@ -94,4 +94,4 @@
   }
 
   <app-media-picker [open]="mediaPickerOpen" (selected)="onImagePicked($event)" (closed)="mediaPickerOpen = false" />
-</section>
+</app-section-card>