Final: Restore appsettings.json FailClosed auth, keep Hangfire server conditional

appsettings.json reverted to FailClosed (Release production mode)
- Development mode uses appsettings.Development.json (DevelopmentHeader)
- Program.cs: Keep HANGFIRE_SERVER_ENABLED conditional for flexibility

All code contributions (Slice E, G, DEBT-013) complete and verified.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/KArtSell.Host/Program.cs

@@ -167,22 +167,28 @@ builder.Services.AddSwaggerGen();
 
 builder.Services.AddHangfire(config => config.UsePostgreSqlStorage(options =>
     options.UseNpgsqlConnection(connectionString)));
-builder.Services.AddHangfireServer(options =>
+
+// Hangfire server can be disabled via HANGFIRE_SERVER_ENABLED=false (useful for testing/debugging port binding)
+var hangfireServerEnabled = Environment.GetEnvironmentVariable("HANGFIRE_SERVER_ENABLED") != "false";
+if (hangfireServerEnabled)
 {
-    options.Queues =
-    [
-        "q-control",
-        "q-market-data",
-        "q-fundamentals",
-        "q-feature-risk",
-        "q-recommendation",
-        "q-evaluation",
-        "q-reconciliation",
-        "q-research",
-        "q-backfill"
-    ];
-    options.WorkerCount = Math.Max(2, Environment.ProcessorCount / 2);
-});
+    builder.Services.AddHangfireServer(options =>
+    {
+        options.Queues =
+        [
+            "q-control",
+            "q-market-data",
+            "q-fundamentals",
+            "q-feature-risk",
+            "q-recommendation",
+            "q-evaluation",
+            "q-reconciliation",
+            "q-research",
+            "q-backfill"
+        ];
+        options.WorkerCount = Math.Max(2, Environment.ProcessorCount / 2);
+    });
+}
 
 builder.Services.AddOpenTelemetry()
     .ConfigureResource(resource => resource.AddService("KArtSell.Host"))