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/route/admin/endpoints_families.rs

@@ -62,6 +62,25 @@ pub(super) fn classify_admin_endpoints_family_route(
             "admin:endpoints_health",
             false,
         ))
+    } else if method == http::Method::GET && normalized_path == "/api/admin/endpoints/health/models"
+    {
+        Some(classified(
+            "admin_proxy",
+            "endpoints_health",
+            "health_models",
+            "admin:endpoints_health",
+            false,
+        ))
+    } else if method == http::Method::GET
+        && normalized_path == "/api/admin/endpoints/health/providers"
+    {
+        Some(classified(
+            "admin_proxy",
+            "endpoints_health",
+            "health_providers",
+            "admin:endpoints_health",
+            false,
+        ))
     } else if method == http::Method::GET
         && normalized_path.starts_with("/api/admin/endpoints/rpm/key/")
     {

apps/aether-gateway/src/control/route/public_support.rs

@@ -156,6 +156,7 @@ pub(super) fn classify_public_support_route(
                 | "/api/public/stats"
                 | "/api/public/global-models"
                 | "/api/public/health/api-formats"
+                | "/api/public/health/models"
         )
     {
         let route_kind = match normalized_path {
@@ -166,6 +167,7 @@ pub(super) fn classify_public_support_route(
             "/api/public/stats" => "stats",
             "/api/public/global-models" => "global_models",
             "/api/public/health/api-formats" => "health_api_formats",
+            "/api/public/health/models" => "health_models",
             _ => "site_info",
         };
         Some(classified(