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.

app/_admin/portfolio/actions.ts

@@ -1,6 +1,6 @@
 "use server";
 
-import { and, eq, inArray } from "drizzle-orm";
+import { eq, inArray } from "drizzle-orm";
 import { revalidatePath } from "next/cache";
 import { redirect } from "next/navigation";
 import { isRedirectError } from "next/dist/client/components/redirect-error";
@@ -154,6 +154,19 @@ export async function upsertCategoryAction(formData: FormData) {
       isActive: normalizeCheckboxValue(formData, "isActive"),
     });
 
+    // Categories and projects share the public `/portfolio/[slug]` route, so a
+    // slug may only exist on one side. Categories win at resolve time, which
+    // would silently hide a project with the same slug.
+    const [projectWithSlug] = await db
+      .select({ id: portfolioProject.id })
+      .from(portfolioProject)
+      .where(eq(portfolioProject.slug, parsed.slug))
+      .limit(1);
+
+    if (projectWithSlug) {
+      throw new Error("Kategorie Slug ist bereits als Projekt Slug vergeben.");
+    }
+
     if (parsed.id) {
       await db.update(category).set(parsed).where(eq(category.id, parsed.id));
     } else {
@@ -172,7 +185,9 @@ export async function upsertCategoryAction(formData: FormData) {
         ? parseZodError(error)
         : isUniqueViolation(error)
           ? "Kategorie Slug muss eindeutig sein."
-          : "Kategorie konnte nicht gespeichert werden.";
+          : error instanceof Error && error.message.includes("Slug")
+            ? error.message
+            : "Kategorie konnte nicht gespeichert werden.";
 
     redirect(withFlash(redirectPath, { error: message }));
   }
@@ -298,6 +313,16 @@ export async function saveProjectAction(formData: FormData) {
       assets,
     });
 
+    const [categoryWithSlug] = await db
+      .select({ id: category.id })
+      .from(category)
+      .where(eq(category.slug, parsed.slug))
+      .limit(1);
+
+    if (categoryWithSlug) {
+      throw new Error("Projekt Slug ist bereits als Kategorie Slug vergeben.");
+    }
+
     const existingProject = parsed.id
       ? (
           await db