test(08-01): add failing RFC 8414 metadata RED test and fail-closed verifier

- wristband.Server.Metadata is a compiling 501 stub; TestPhase8RedMetadata
  asserts the exact unwrapped PHP metadata document, headers and status and
  fails with the PHASE8_RED:metadata sentinel (D-06)
- scripts/check-phase8-red.sh implements the shared go/shell RED contract
  for the rest of Phase 8: exact selected test/package failure plus sentinel,
  rejecting unrelated fail actions, compile/setup failures, panics,
  malformed JSON, missing/duplicate sentinels and zero selection (D-04/D-18)

wristband/server_test.go

@@ -0,0 +1,39 @@
+package wristband
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// TestPhase8RedMetadata is the Phase 8 Wave 1 RED anchor (08-CONTEXT.md
+// D-06). It asserts the exact unwrapped RFC 8414 metadata document recorded
+// from the live PHP fixture (parity/fixtures/routes/GET__.well-known_oauth-authorization-server_oauth.yaml)
+// and fails with the PHASE8_RED:metadata sentinel while Server.Metadata is a
+// stub. scripts/check-phase8-red.sh verifies this failure is fail-closed.
+func TestPhase8RedMetadata(t *testing.T) {
+	opts := DefaultOptions()
+	opts.Issuer = "https://plytarium.com"
+	srv := NewServer(opts)
+
+	req := httptest.NewRequest(http.MethodGet, "/.well-known/oauth-authorization-server", nil)
+	req.Header.Set("Accept", "application/json")
+	rec := httptest.NewRecorder()
+	srv.Metadata(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("PHASE8_RED:metadata: status = %d, want %d", rec.Code, http.StatusOK)
+	}
+
+	const want = `{"issuer":"https://plytarium.com","authorization_endpoint":"https://plytarium.com/oauth/mcp/authorize","token_endpoint":"https://plytarium.com/oauth/mcp/token","registration_endpoint":"https://plytarium.com/oauth/mcp/register","response_types_supported":["code"],"grant_types_supported":["authorization_code","refresh_token"],"code_challenge_methods_supported":["S256"],"token_endpoint_auth_methods_supported":["none","client_secret_post","client_secret_basic"],"scopes_supported":["read","write","ai","offline_access"],"service_documentation":"https://plytarium.com/help","authorization_response_iss_parameter_supported":true}`
+
+	if got := rec.Body.String(); got != want {
+		t.Fatalf("PHASE8_RED:metadata: body mismatch\n got:  %s\nwant: %s", got, want)
+	}
+	if ct := rec.Header().Get("Content-Type"); ct != "application/json" {
+		t.Fatalf("PHASE8_RED:metadata: Content-Type = %q, want application/json", ct)
+	}
+	if cc := rec.Header().Get("Cache-Control"); cc != "no-cache, private" {
+		t.Fatalf("PHASE8_RED:metadata: Cache-Control = %q, want \"no-cache, private\"", cc)
+	}
+}