feat(health): add model and provider health monitoring

- Rename the original health monitor to endpoint health monitor
- Add tab navigation for endpoint, model, and provider health views
- Add model health monitor cards with availability, latency, first-byte latency, and 60-point history
- Add admin-only provider health monitor with collapsible active-provider sections
- Show per-provider model health cards after expanding a provider
- Add backend model health and provider health monitor payload builders
- Add admin endpoint for provider health monitoring
- Add provider-scoped usage breakdown filtering for per-provider model statistics
- Add frontend API types and request helpers for model/provider health data
- Add demo mock data for model and provider health monitoring
- Fix model health timeline time-unit handling so request history segments render correctly

Verification:
- cargo fmt
- npm run type-check
- npm run build
- cargo test -p aether-gateway health_models
- cargo test -p aether-gateway health_providers
- cargo test -p aether-gateway gateway_exposes_frontdoor_manifest_without_proxying_upstream

apps/aether-gateway/src/control/tests/admin_endpoints.rs

@@ -102,6 +102,44 @@ fn classifies_admin_endpoint_health_status_as_admin_proxy_route() {
     assert!(!decision.is_execution_runtime_candidate());
 }
 
+#[test]
+fn classifies_admin_endpoint_health_models_as_admin_proxy_route() {
+    let headers = headers(&[]);
+    let uri: Uri = "/api/admin/endpoints/health/models?lookback_hours=12"
+        .parse()
+        .expect("uri should parse");
+    let decision =
+        classify_control_route(&http::Method::GET, &uri, &headers).expect("route should classify");
+
+    assert_eq!(decision.route_class.as_deref(), Some("admin_proxy"));
+    assert_eq!(decision.route_family.as_deref(), Some("endpoints_health"));
+    assert_eq!(decision.route_kind.as_deref(), Some("health_models"));
+    assert_eq!(
+        decision.auth_endpoint_signature.as_deref(),
+        Some("admin:endpoints_health")
+    );
+    assert!(!decision.is_execution_runtime_candidate());
+}
+
+#[test]
+fn classifies_admin_endpoint_health_providers_as_admin_proxy_route() {
+    let headers = headers(&[]);
+    let uri: Uri = "/api/admin/endpoints/health/providers?lookback_hours=12"
+        .parse()
+        .expect("uri should parse");
+    let decision =
+        classify_control_route(&http::Method::GET, &uri, &headers).expect("route should classify");
+
+    assert_eq!(decision.route_class.as_deref(), Some("admin_proxy"));
+    assert_eq!(decision.route_family.as_deref(), Some("endpoints_health"));
+    assert_eq!(decision.route_kind.as_deref(), Some("health_providers"));
+    assert_eq!(
+        decision.auth_endpoint_signature.as_deref(),
+        Some("admin:endpoints_health")
+    );
+    assert!(!decision.is_execution_runtime_candidate());
+}
+
 #[test]
 fn classifies_admin_endpoint_key_rpm_as_admin_proxy_route() {
     let headers = headers(&[]);