fix(seed): IgnoreQueryFilters on all seeder queries + sitemap invalid date guard

DemoSeedService / DemoMenuSeeder:
  Add IgnoreQueryFilters() to every seeder lookup (Taxes, MenuCategories,
  MenuItems). Soft-deleted rows still hold their PKs; without this a second
  seed run after user-deletion throws a PK collision on the Tax or category
  that was soft-deleted but is still in the index.

sitemap.ts:
  Guard new Date(post.date) against empty / missing frontmatter date fields.
  new Date("") = Invalid Date → broken <lastmod> in sitemap XML.
  Fall back to the build-time date when the post date is absent or invalid.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/website/src/app/sitemap.ts

@@ -42,9 +42,10 @@ export default function sitemap(): MetadataRoute.Sitemap {
 
     const posts = getAllPosts(locale);
     for (const post of posts) {
+      const postDate = post.date ? new Date(post.date) : null;
       entries.push({
         url: `${BASE_URL}/${locale}/blog/${post.slug}`,
-        lastModified: new Date(post.date),
+        lastModified: postDate && !isNaN(postDate.getTime()) ? postDate : now,
         changeFrequency: "monthly",
         priority: 0.7,
       });