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- DapperOutboxMessageReader: Remove cutoffTime parameter, process ALL unpublished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- Tests: Remove cutoff scenario (no longer applicable); keep normal + max-attempts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.BuildingBlocks/Reliability/DapperOutboxMessageReader.cs

@@ -17,7 +17,6 @@ public sealed class DapperOutboxMessageReader(IDbConnectionFactory connectionFac
             attempt as Attempt
         from building_blocks.outbox_message
         where published_at is null
-          and occurred_at >= @CutoffTime
         order by occurred_at asc
         limit @BatchSize
         """;
@@ -36,7 +35,6 @@ public sealed class DapperOutboxMessageReader(IDbConnectionFactory connectionFac
         """;
 
     public async Task<IReadOnlyList<OutboxMessageRow>> GetUnpublishedAsync(
-        DateTimeOffset cutoffTime,
         int batchSize,
         CancellationToken cancellationToken)
     {
@@ -44,7 +42,7 @@ public sealed class DapperOutboxMessageReader(IDbConnectionFactory connectionFac
         var messages = await connection.QueryAsync<OutboxMessageRow>(
             new CommandDefinition(
                 SelectUnpublishedSql,
-                new { CutoffTime = cutoffTime, BatchSize = batchSize },
+                new { BatchSize = batchSize },
                 cancellationToken: cancellationToken));
         return messages.ToList();
     }