fix: restore dark theme tokens for login/admin/legal pages + remove formation SEO

- globals.css: restore missing dark-*, primary, error, warning color tokens
  and gradient-text/gradient-bg utility classes so login, admin, mentions-legales,
  and confidentialite pages render correctly (white text was invisible on white bg)
- layout.tsx: remove "Candidature Formation" from JSON-LD SiteNavigationElement
- candidature/layout.tsx: remove "Formation" from title/description, add noindex
- robots.ts: disallow /candidature/ from crawlers
- sitemap.ts: remove /candidature from sitemap

https://claude.ai/code/session_01V8YAjpqRQ3bfBYsABYsEgo

app/robots.ts

@@ -8,7 +8,7 @@ export default function robots(): MetadataRoute.Robots {
       {
         userAgent: "*",
         allow: "/",
-        disallow: ["/admin/", "/api/", "/setup-admin/", "/dashboard/", "/profil/", "/formations/", "/login/", "/register/"],
+        disallow: ["/admin/", "/api/", "/setup-admin/", "/dashboard/", "/profil/", "/formations/", "/login/", "/register/", "/candidature/"],
       },
     ],
     sitemap: `${BASE_URL}/sitemap.xml`,