feat: add Keycloak authentication for dashboard and API endpoints (#2)

Dashboard: OAuth2/OIDC login flow with PKCE, session-based auth middleware
protecting all server function endpoints, check-auth server function for
frontend auth state, login page gate in AppShell, user info in sidebar.

Agent API: JWT validation middleware using Keycloak JWKS endpoint,
conditionally enabled when KEYCLOAK_URL and KEYCLOAK_REALM are set.

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

Co-authored-by: Sharang Parnerkar <parnerkarsharang@gmail.com>
Reviewed-on: #2

compliance-agent/src/api/server.rs

@@ -1,19 +1,37 @@
 use std::sync::Arc;
 
-use axum::Extension;
+use axum::{middleware, Extension};
+use tokio::sync::RwLock;
 use tower_http::cors::CorsLayer;
 use tower_http::trace::TraceLayer;
 
 use crate::agent::ComplianceAgent;
+use crate::api::auth_middleware::{require_jwt_auth, JwksState};
 use crate::api::routes;
 use crate::error::AgentError;
 
 pub async fn start_api_server(agent: ComplianceAgent, port: u16) -> Result<(), AgentError> {
-    let app = routes::build_router()
-        .layer(Extension(Arc::new(agent)))
+    let mut app = routes::build_router()
+        .layer(Extension(Arc::new(agent.clone())))
         .layer(CorsLayer::permissive())
         .layer(TraceLayer::new_for_http());
 
+    if let (Some(kc_url), Some(kc_realm)) =
+        (&agent.config.keycloak_url, &agent.config.keycloak_realm)
+    {
+        let jwks_url = format!("{kc_url}/realms/{kc_realm}/protocol/openid-connect/certs");
+        let jwks_state = JwksState {
+            jwks: Arc::new(RwLock::new(None)),
+            jwks_url,
+        };
+        tracing::info!("Keycloak JWT auth enabled for realm '{kc_realm}'");
+        app = app
+            .layer(Extension(jwks_state))
+            .layer(middleware::from_fn(require_jwt_auth));
+    } else {
+        tracing::warn!("Keycloak not configured - API endpoints are unprotected");
+    }
+
     let addr = format!("0.0.0.0:{port}");
     let listener = tokio::net::TcpListener::bind(&addr)
         .await