phase-5: add runtime theme and branding engine services

src/app/theme/runtime/branding-engine.service.ts

@@ -0,0 +1,36 @@
+import { DOCUMENT } from '@angular/common';
+import { Injectable, inject } from '@angular/core';
+import { take } from 'rxjs/operators';
+import { ConfigService } from '../../core/config/config.service';
+import { BrandingConfig } from '../../shared/models/config';
+
+@Injectable({ providedIn: 'root' })
+export class BrandingEngineService {
+  private readonly document = inject(DOCUMENT);
+  private readonly configService = inject(ConfigService);
+
+  initialize(): void {
+    this.configService.loadBootstrap().pipe(take(1)).subscribe({
+      next: (bootstrap) => this.applyBranding(bootstrap.branding),
+      error: () => {
+        // Branding bootstrapping should not break app startup.
+      }
+    });
+  }
+
+  applyBranding(branding: BrandingConfig): void {
+    const root = this.document.documentElement;
+    root.style.setProperty('--brand-logo-url', `url('${branding.logoUrl}')`);
+    root.style.setProperty('--brand-logo-compact-url', `url('${branding.logoCompactUrl ?? branding.logoUrl}')`);
+
+    const existing = this.document.querySelector("link[rel='icon']") as HTMLLinkElement | null;
+    if (existing) {
+      existing.href = branding.faviconUrl;
+    } else {
+      const link = this.document.createElement('link');
+      link.rel = 'icon';
+      link.href = branding.faviconUrl;
+      this.document.head.appendChild(link);
+    }
+  }
+}