feat: Page Editor UX Phase 2 - unsaved changes panel, property search, reset property, empty states

- ProjectEditorFacade.resetField(key): field-level revert-to-original, reusing getByPath + a new immutable setByPath (write-side counterpart, scalar/object dot-paths only).
- app-form-field gains showReset/resetLabel/(resetClicked) - a reusable per-field reset affordance, wired on branding logo/title and theme primary/background color.
- Save bar: unsaved-changes count is now clickable, expanding a field-level diff list (reuses facade.changeSummary(), already built for the Preview tab) with jump-to-section links.
- BuilderPropertySearchComponent: filters EditorSchemaService.all() by translated label/hint, jumps to the owning section - no new registry, reuses the existing schema.
- navigation-section: app-empty-state (existing component) added for empty header/footer link lists.
- Reset Section and Draft/Published badge were already implemented; not touched.
- New copy added as translation keys (en/ru/hy).

src/app/i18n/translations.ts

@@ -881,6 +881,16 @@ export interface Translations {
     usedByLinks: string;
     usedByBadges: string;
     usedByPageBackground: string;
+    resetField: string;
+    propertySearchLabel: string;
+    propertySearchPlaceholder: string;
+    propertySearchResultsLabel: string;
+    propertySearchNoResults: string;
+    unsavedChangesPanelTitle: string;
+    navigationHeaderEmptyTitle: string;
+    navigationHeaderEmptyDesc: string;
+    navigationFooterEmptyTitle: string;
+    navigationFooterEmptyDesc: string;
     blockRemoveConfirm: string;
     blockHero: string;
     blockHeroDesc: string;