fix: Hangfire distributed lock timeout resilience + Gate 3 execution

- Program.cs: Wrap recurring job registration in try-catch to handle distributed lock timeouts
  Allows Host to start even if Hangfire lock is stuck (may be acquired by another instance)
- Add gate3_rehearsal.ps1 for Shadow Run rehearsal validation
- Set ASPNETCORE_ENVIRONMENT=Development to enable DevelopmentHeaderAuthenticationHandler
- Gate 3 Shadow Run now executing: 252+ trading-day validation with real KRX data

Status:
  ✅ Host ready (Development mode, port 5002)
  ✅ Shadow Run created (ID: d14f34ea-2afe-4caf-bbb1-c9a7d74fb582)
  ⏳ Execution in progress (ETA ~60 minutes)

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

src/KArtSell.Host/Program.cs

@@ -215,17 +215,35 @@ app.MapHub<KArtSell.Host.Consumers.ShadowRunHub>("/api/hubs/shadow-run");
 
 app.Services.RegisterModelOperationsSchedules(modelOperationsDispatcherEnabled, modelOperationsDispatcherCron);
 
-RecurringJob.AddOrUpdate<OutboxPollerJob>(
-    "outbox-poller",
-    job => job.ExecuteAsync(CancellationToken.None),
-    "* * * * *",
-    new RecurringJobOptions { TimeZone = TimeZoneInfo.Utc });
+// Register recurring jobs with timeout resilience (Hangfire distributed lock may be stuck)
+var logger = app.Services.GetRequiredService<ILogger<Program>>();
+try
+{
+    RecurringJob.AddOrUpdate<OutboxPollerJob>(
+        "outbox-poller",
+        job => job.ExecuteAsync(CancellationToken.None),
+        "* * * * *",
+        new RecurringJobOptions { TimeZone = TimeZoneInfo.Utc });
+    logger.LogInformation("✅ Recurring job 'outbox-poller' registered");
+}
+catch (Exception ex) when (ex.Message.Contains("Timeout"))
+{
+    logger.LogWarning(ex, "⚠️ Hangfire lock timeout registering outbox-poller; job may be registered by another instance or lock is stuck");
+}
 
-RecurringJob.AddOrUpdate<DownstreamConsumerJob>(
-    "downstream-consumer",
-    job => job.ExecuteAsync(CancellationToken.None),
-    "* * * * *",
-    new RecurringJobOptions { TimeZone = TimeZoneInfo.Utc });
+try
+{
+    RecurringJob.AddOrUpdate<DownstreamConsumerJob>(
+        "downstream-consumer",
+        job => job.ExecuteAsync(CancellationToken.None),
+        "* * * * *",
+        new RecurringJobOptions { TimeZone = TimeZoneInfo.Utc });
+    logger.LogInformation("✅ Recurring job 'downstream-consumer' registered");
+}
+catch (Exception ex) when (ex.Message.Contains("Timeout"))
+{
+    logger.LogWarning(ex, "⚠️ Hangfire lock timeout registering downstream-consumer; job may be registered by another instance or lock is stuck");
+}
 
 // OpenDart daily batch (KST timezone, market open 09:00)
 var kstTimeZone = TimeZoneInfo.FindSystemTimeZoneById("Asia/Seoul");