ADDED - Admin SEO page, robots/sitemap hardening and media/maintenance security fixes

SEO
- New Settings > SEO admin page (seo_settings in app_config): indexing switch,
  Google/Bing verification, X handle, JSON-LD identity (Person/Organization,
  sameAs), per-locale keywords, readiness checklist and open links for
  sitemap.xml / robots.txt / manifest.
- robots.txt is now dynamic: disallows admin, api, success and coming-soon
  paths; blocks everything while indexing is off or maintenance is on.
- sitemap.xml carries hreflang alternates per URL, lists only categories with
  published projects, and is empty while hidden.
- Metadata: robots + verification meta, og:locale in de_DE/en_US/ar_AR form,
  alternateLocale, twitter site/creator, project cover as OG image with
  article type, noindex on /success and /coming-soon.
- JSON-LD: WebSite + publisher graph on all public pages, CreativeWork per
  project (view-mode independent).

Security
- Maintenance bypass now requires a correctly signed admin cookie; the
  middleware previously only checked the cookie existed. Token helpers moved
  to lib/admin-session-token.ts (shared by proxy.ts and lib/admin-auth.ts).
- Media uploads: magic-byte validation against the declared type, SVG
  sanitization (script/handlers/foreignObject/javascript: rejected), upload
  folder sanitized, kind inferred from the real file.
- Media route: fixed prefix-based path check that accepted sibling
  directories, unknown extensions return 404, nosniff header, CSP sandbox on
  SVG, gif content type added.
- External media URLs: protocol-relative (//host) URLs rejected.

Portfolio
- Project and category slugs share /portfolio/[slug]; saving now rejects a
  slug already used on the other side instead of silently shadowing it.

Tooling/docs
- Lint: ignore scripts/legacy-prisma-seed.cjs, drop unused import.
- New docs/SEO.md; FEATURES, ARCHITECTURE (Drizzle instead of Prisma), admin
  spec and CLAUDE.md updated.
- Tests for all of the above (unit + integration); suite green.

tests/integration/actions-portfolio.test.ts

@@ -104,6 +104,14 @@ describe("upsertCategoryAction", () => {
     expect(category?.nameEn).toBe("Renamed");
   });
 
+  it("rejects a category slug that already belongs to a project", async () => {
+    const other = await createCategory({ slug: "other" });
+    await createProject({ categoryId: other.id, slug: "taken" });
+    const url = await captureRedirect(() => upsertCategoryAction(categoryForm({ slug: "taken" })));
+    expect(new URL(url, "http://test").searchParams.get("error")).toContain("Projekt Slug vergeben");
+    expect(await db.query.category.findFirst({ where: eq(categoryTable.slug, "taken") })).toBeUndefined();
+  });
+
   it("reports a unique-constraint violation on duplicate slugs", async () => {
     await createCategory({ slug: "branding" });
     const url = await captureRedirect(() => upsertCategoryAction(categoryForm({ slug: "branding" })));
@@ -141,6 +149,13 @@ describe("deleteCategoryAction", () => {
 });
 
 describe("saveProjectAction", () => {
+  it("rejects a project slug that already belongs to a category", async () => {
+    const category = await createCategory({ slug: "branding" });
+    const url = await captureRedirect(() => saveProjectAction(projectForm(category.id, { slug: "branding" })));
+    expect(new URL(url, "http://test").searchParams.get("error")).toContain("Kategorie Slug vergeben");
+    expect(await db.query.portfolioProject.findFirst({ where: eq(portfolioProjectTable.slug, "branding") })).toBeUndefined();
+  });
+
   it("creates a published project with cover and asset media usages", async () => {
     const category = await createCategory();
     const url = await captureRedirect(() => saveProjectAction(projectForm(category.id)));