feat: add DaisyUI v5 theming, PKCE auth, and Keycloak realm export

- Add DaisyUI v5 with custom certifai-dark/certifai-light themes using oklch colors
- Create styles/input.css as Tailwind + DaisyUI entry point (replaces root tailwind.css)
- Add SVG brand logo combining shield motif with neural network nodes
- Implement PKCE (S256) for OAuth authorization code flow
- Add Keycloak realm-export.json with test users for local development
- Fix CSS load order in app.rs (tailwind before main.css) and add data-theme attribute

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

.gitignore

@@ -12,5 +12,9 @@
 # Logs
 *.log
 
-# Keycloak data
-keycloak/
+# Keycloak runtime data (but keep realm-export.json)
+keycloak/*
+!keycloak/realm-export.json
+
+# Node modules
+node_modules/