feat(auth): add custom Keycloak login theme matching dashboard

Branded Keycloak login page with CERTifAI dark theme: indigo/teal
color palette, Inter + Space Grotesk fonts, animated background
gradients, card glow, logo float, and button shimmer effects.
Overrides PatternFly v4 defaults including autofill color fix.

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

keycloak/realm-export.json

@@ -9,6 +9,7 @@
   "loginWithEmailAllowed": true,
   "duplicateEmailsAllowed": false,
   "resetPasswordAllowed": true,
+  "loginTheme": "certifai",
   "editUsernameAllowed": false,
   "bruteForceProtected": true,
   "permanentLockout": false,