fix(reliability): Remove cutoffTime filter to prevent data loss in outbox poller

CRITICAL: Previous cutoffTime logic (occurred_at >= now-5min) silently dropped
messages older than 5 minutes forever, contradicting Outbox Pattern's guarantee
of eventual delivery for stuck messages.

Changes:
- DapperOutboxMessageReader: Remove cutoffTime parameter, process ALL unpublished
- OutboxPollerJob: Remove cutoffTime calculation, process all messages by occurred_at
- Tests: Remove cutoff scenario (no longer applicable); keep normal + max-attempts
- Comments: Document monitoring approach (alert if pending > 5 min) as separate concern

AGENTS.md v16.0 Checklist:
✅ Safety: No partial success (no silent data loss)
✅ Audit: Evidence tracked (all messages eventually processed)
✅ Right Way: Root cause fixed (was processing-logic bug, not test-logic bug)

Test results: 2/2 passing (normal path, max-attempts DQ)
Validation gate: Outbox/Inbox crash-recovery ✅ RESTORED

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

src/KArtSell.Host/Jobs/OutboxPollerJob.cs

@@ -43,9 +43,10 @@ public sealed class OutboxPollerJob(
     public async Task ExecuteAsync(CancellationToken cancellationToken = default)
     {
         var now = clock.UtcNow;
-        var cutoffTime = now.AddMinutes(-5);
 
-        var messages = await reader.GetUnpublishedAsync(cutoffTime, DefaultBatchSize, cancellationToken);
+        // Process all unpublished messages ordered by occurred_at (oldest first).
+        // Monitoring: alert if any message pending > 5 min (see dashboard/alerts).
+        var messages = await reader.GetUnpublishedAsync(DefaultBatchSize, cancellationToken);
 
         var failureCount = 0;
         foreach (var message in messages)