WP-40/41/42: dashboard, security hardening, deployment and operations docs

Dashboard endpoint and page aggregating inventory, vulnerabilities, cluster
health, backups and recent jobs. Security headers (CSP, nosniff, DENY,
referrer policy), 1 MB body limit, configurable login rate limit, audit
steps in CI. Installer script, systemd unit, install/architecture docs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/crates/api/tests/security.rs

@@ -0,0 +1,72 @@
+//! WP-41: security headers and cookie hardening.
+mod common;
+
+use axum::http::StatusCode;
+use common::{get, post, test_app_with_admin};
+use serde_json::json;
+
+#[tokio::test]
+async fn responses_carry_security_headers() {
+    let app = test_app_with_admin().await;
+    let res = get(&app, "/healthz", None).await;
+    let h = |k: &str| {
+        res.headers
+            .get(k)
+            .and_then(|v| v.to_str().ok())
+            .unwrap_or("")
+            .to_string()
+    };
+    assert_eq!(h("x-content-type-options"), "nosniff");
+    assert_eq!(h("x-frame-options"), "DENY");
+    assert_eq!(h("referrer-policy"), "same-origin");
+    let csp = h("content-security-policy");
+    assert!(csp.contains("default-src 'self'"), "{csp}");
+    assert!(csp.contains("frame-ancestors 'none'"), "{csp}");
+    assert_eq!(h("cache-control"), "no-store");
+    assert!(res.headers.get("server").is_none());
+
+    // API errors are JSON, not HTML, and still carry the headers
+    let res = get(&app, "/api/users", None).await;
+    assert_eq!(res.status, StatusCode::UNAUTHORIZED);
+    assert_eq!(res.json["error"], "unauthorized");
+    assert_eq!(
+        res.headers.get("x-content-type-options").unwrap(),
+        "nosniff"
+    );
+}
+
+#[tokio::test]
+async fn refresh_cookie_is_strict_and_scoped() {
+    let app = test_app_with_admin().await;
+    let res = post(
+        &app,
+        "/api/auth/login",
+        json!({"email": "admin@example.com", "password": "admin-password-123"}),
+        None,
+    )
+    .await;
+    let cookie = res.headers.get("set-cookie").unwrap().to_str().unwrap();
+    assert!(
+        cookie.contains("HttpOnly")
+            && cookie.contains("SameSite=Strict")
+            && cookie.contains("Path=/api/auth")
+    );
+    // cross-site style request without the cookie cannot refresh
+    assert_eq!(
+        post(&app, "/api/auth/refresh", json!({}), None)
+            .await
+            .status,
+        StatusCode::UNAUTHORIZED
+    );
+}
+
+#[tokio::test]
+async fn oversized_json_bodies_are_rejected() {
+    let app = test_app_with_admin().await;
+    let token = common::login(&app, "admin@example.com", "admin-password-123")
+        .await
+        .access;
+    let big = "x".repeat(2 * 1024 * 1024);
+    let res = post(&app, "/api/users", json!({"email": "a@b.de", "display_name": big, "password": "user-password-123", "role": "user"}), Some(&token)).await;
+    assert_eq!(res.status, StatusCode::PAYLOAD_TOO_LARGE);
+}