[router] Configure experimental sgl-router via CLI flags instead of a config file (#27073)

Signed-off-by: Kangyan Zhou <zky314343421@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

experimental/sgl-router/tests/proxy/failover.rs

@@ -31,7 +31,7 @@ async fn failover_when_one_worker_dies() {
             port: 0,
         },
         observability: Default::default(),
-        models: vec![ModelConfig {
+        model: ModelConfig {
             id: "tiny".into(),
             tokenizer_path: "tests/fixtures/tiny_tokenizer.json".into(),
             policy: PolicyKind::RoundRobin,
@@ -40,12 +40,10 @@ async fn failover_when_one_worker_dies() {
                 cool_down_secs: 30,
             }),
             cache_aware: None,
-        }],
-        discovery: DiscoveryConfig {
-            backend: DiscoveryBackend::StaticUrls(StaticUrlsDiscoveryConfig {
-                urls: vec![w1.url.clone(), w2.url.clone(), w3.url.clone()],
-            }),
         },
+        discovery: DiscoveryBackend::StaticUrls(StaticUrlsDiscoveryConfig {
+            urls: vec![w1.url.clone(), w2.url.clone(), w3.url.clone()],
+        }),
         proxy: ProxyConfig::default(),
         active_load: ActiveLoadConfig::default(),
     };