fix(static-pages): stop createPage/duplicatePage from generating colliding slugs/routes

createPage() derived its slug from array length (custom-page-${length+1}):
create, delete, create again reliably reproduces a duplicate slug against a
surviving page. duplicatePage() had the same issue with a fixed '-copy'
suffix - duplicating the same page twice collides with the first duplicate.
Both trip the duplicate-slug/route validator on a page the user never
directly touched.

Added uniqueValue() (append -2, -3, ... until free) and used it for both.
Verified live via window.ng.getComponent(): reproduced the exact collision
scenario pre-fix, confirmed no duplicates post-fix (custom-page-6-2,
about-us-copy/about-us-copy-2).

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

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

@@ -156,8 +156,28 @@ export class StaticPagesEditorComponent {
     this.mediaPickerOpen = false;
   }
 
+  /**
+   * Appends `-2`, `-3`, ... to `candidate` until it's not in `existing`.
+   * createPage()/duplicatePage() both used to derive slugs/routes from array
+   * length or a fixed "-copy" suffix, which reproducibly collides with an
+   * existing page (create, delete, create again; or duplicate the same page
+   * twice) - the duplicate then trips the duplicate-slug/route validator
+   * on a page the user never touched.
+   */
+  private uniqueValue(candidate: string, existing: Set<string>): string {
+    if (!existing.has(candidate)) {
+      return candidate;
+    }
+    let suffix = 2;
+    while (existing.has(`${candidate}-${suffix}`)) {
+      suffix++;
+    }
+    return `${candidate}-${suffix}`;
+  }
+
   createPage(): void {
-    const slug = `custom-page-${this.allPages().length + 1}`;
+    const existingSlugs = new Set(this.allPages().map(page => page.slug));
+    const slug = this.uniqueValue(`custom-page-${this.allPages().length + 1}`, existingSlugs);
     const page: ContentPage = {
       id: `page-${Date.now()}`,
       slug,
@@ -189,11 +209,13 @@ export class StaticPagesEditorComponent {
     if (!source) {
       return;
     }
+    const existingSlugs = new Set(this.allPages().map(page => page.slug));
+    const existingRoutes = new Set(this.allPages().map(page => page.route));
     const clone: ContentPage = {
       ...source,
       id: `page-${Date.now()}`,
-      slug: `${source.slug}-copy`,
-      route: `${source.route}-copy`,
+      slug: this.uniqueValue(`${source.slug}-copy`, existingSlugs),
+      route: this.uniqueValue(`${source.route}-copy`, existingRoutes),
       order: this.allPages().length + 1,
       status: 'draft',
       translations: Object.fromEntries(Object.entries(source.translations).map(([locale, t]) => [locale, { ...t }])),