feat(project-editor): live inline validation and publish gating

Milestone 3 of the Configuration Engine sprint.

- Facade fieldError(key) accessor over issuesByField for inline field errors.
- Bind [error] on schema-backed fields: theme palette colours, general
  name/domain, branding logo (translated via each section).
- project-editor-nav: per-section blocking-issue count badge (issuesBySection).
- save-bar: Publish now disabled on hasBlockingIssues() (errors only, so new
  warnings no longer block); issue list tags warning vs error severity.

Editor verified rendering at /ru/edit/theme with the new nav + save bar;
validation logic covered by the 25 unit tests.

Gate: tsc --noEmit, npm test (25/25), arch:check, build all green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -2,6 +2,7 @@ import { ChangeDetectionStrategy, Component, computed, inject } from '@angular/c
 import { FormsModule } from '@angular/forms';
 import { ProjectEditorFacade } from '../facade/project-editor.facade';
 import { TranslatePipe } from '../../../i18n/translate.pipe';
+import { TranslateService } from '../../../i18n/translate.service';
 import { InputComponent } from '../../../shared/ui/input/input.component';
 import { FormFieldComponent } from '../../../shared/ui/form-field/form-field.component';
 import { SectionCardComponent } from '../../../shared/ui/section-card/section-card.component';
@@ -16,7 +17,12 @@ import { SectionCardComponent } from '../../../shared/ui/section-card/section-ca
 })
 export class ProjectEditorGeneralSectionComponent {
   private readonly facade = inject(ProjectEditorFacade);
+  private readonly translate = inject(TranslateService);
   readonly bootstrap = this.facade.bootstrap;
+  readonly fieldError = (key: string): string | null => {
+    const messageKey = this.facade.fieldError(key);
+    return messageKey ? this.translate.t(messageKey) : null;
+  };
   readonly languagesValue = computed(() => (this.bootstrap()?.localization.supportedLocales ?? []).join(', '));
 
   updateMarketplaceName(value: string): void {