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/unit/admin-session-token.test.ts

@@ -0,0 +1,39 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+
+import { buildAdminSessionToken, verifyAdminSessionToken } from "@/lib/admin-session-token";
+
+const originalSecret = process.env.ADMIN_AUTH_SECRET;
+
+beforeEach(() => {
+  process.env.ADMIN_AUTH_SECRET = "unit-test-secret";
+});
+
+afterEach(() => {
+  process.env.ADMIN_AUTH_SECRET = originalSecret;
+});
+
+describe("admin session token", () => {
+  it("round-trips a signed token", () => {
+    expect(verifyAdminSessionToken(buildAdminSessionToken())).toBe(true);
+  });
+
+  it("rejects forged, malformed, or missing tokens", () => {
+    expect(verifyAdminSessionToken("superadmin")).toBe(false);
+    expect(verifyAdminSessionToken("superadmin.deadbeef")).toBe(false);
+    expect(verifyAdminSessionToken("other." + buildAdminSessionToken().split(".")[1])).toBe(false);
+    expect(verifyAdminSessionToken("")).toBe(false);
+    expect(verifyAdminSessionToken(undefined)).toBe(false);
+    expect(verifyAdminSessionToken("1")).toBe(false);
+  });
+
+  it("rejects a token signed with a different secret", () => {
+    const token = buildAdminSessionToken();
+    process.env.ADMIN_AUTH_SECRET = "rotated";
+    expect(verifyAdminSessionToken(token)).toBe(false);
+  });
+
+  it("never validates when no secret is configured", () => {
+    process.env.ADMIN_AUTH_SECRET = "";
+    expect(verifyAdminSessionToken("superadmin.anything")).toBe(false);
+  });
+});