[router] Speak cleartext h2c on both edges: serve it inbound, forward it outbound (#39006)

Co-authored-by: Kangyan Zhou <kangyan.zhou@radixark.ai>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

experimental/sgl-router/Cargo.lock

@@ -2887,6 +2887,7 @@ dependencies = [
  "bytes",
  "futures-core",
  "futures-util",
+ "h2",
  "http",
  "http-body",
  "http-body-util",
@@ -3294,6 +3295,8 @@ dependencies = [
  "futures",
  "hf-hub",
  "http-body-util",
+ "hyper",
+ "hyper-util",
  "k8s-openapi",
  "kube",
  "minijinja",