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/handlers/public/support.rs

@@ -1,9 +1,10 @@
 use super::{
-    build_api_format_health_monitor_payload, build_public_auth_modules_status_payload,
-    build_public_catalog_models_payload, build_public_catalog_search_models_payload,
-    build_public_providers_payload, capability_detail_by_name, ldap_module_config_is_valid,
-    sanitize_public_model_config_for_user, serialize_public_capability, supported_capability_names,
-    ApiFormatHealthMonitorOptions, PUBLIC_CAPABILITY_DEFINITIONS,
+    build_api_format_health_monitor_payload, build_model_health_monitor_payload,
+    build_public_auth_modules_status_payload, build_public_catalog_models_payload,
+    build_public_catalog_search_models_payload, build_public_providers_payload,
+    capability_detail_by_name, ldap_module_config_is_valid, sanitize_public_model_config_for_user,
+    serialize_public_capability, supported_capability_names, ApiFormatHealthMonitorOptions,
+    ModelHealthMonitorOptions, PUBLIC_CAPABILITY_DEFINITIONS,
 };
 use crate::control::GatewayPublicRequestContext;
 use crate::handlers::shared::{
@@ -426,6 +427,43 @@ pub(crate) async fn maybe_build_local_public_support_response(
             .await?;
             return Some(Json(payload).into_response());
         }
+
+        if decision.route_kind.as_deref() == Some("health_models")
+            && request_context.request_path == "/api/public/health/models"
+        {
+            let lookback_hours = query_param_value(
+                request_context.request_query_string.as_deref(),
+                "lookback_hours",
+            )
+            .and_then(|value| value.parse::<u64>().ok())
+            .filter(|value| (1..=168).contains(value))
+            .unwrap_or(6);
+            let model_limit = query_param_value(
+                request_context.request_query_string.as_deref(),
+                "model_limit",
+            )
+            .and_then(|value| value.parse::<usize>().ok())
+            .filter(|value| (1..=50).contains(value))
+            .unwrap_or(12);
+            let per_model_limit = query_param_value(
+                request_context.request_query_string.as_deref(),
+                "per_model_limit",
+            )
+            .and_then(|value| value.parse::<usize>().ok())
+            .filter(|value| (10..=500).contains(value))
+            .unwrap_or(100);
+            let payload = build_model_health_monitor_payload(
+                state,
+                lookback_hours,
+                model_limit,
+                per_model_limit,
+                ModelHealthMonitorOptions {
+                    include_provider_count: false,
+                },
+            )
+            .await?;
+            return Some(Json(payload).into_response());
+        }
     }
 
     if decision.route_family.as_deref() == Some("capabilities") {