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>

Cargo.lock

@@ -739,6 +739,7 @@ version = "0.1.0"
 dependencies = [
  "async-stripe",
  "axum",
+ "base64 0.22.1",
  "chrono",
  "dioxus",
  "dioxus-cli-config",
@@ -755,6 +756,7 @@ dependencies = [
  "secrecy",
  "serde",
  "serde_json",
+ "sha2",
  "thiserror 2.0.18",
  "time",
  "tokio",