fix: Restore idempotency for recommendation report jobs

**Problem:** Previous commit stubbed HasReportBeenSentAsync/MarkReportSentAsync due to Dapper AOT error, but didn't restore idempotency check/mark calls. This broke CLAUDE.md guarantee: "Each job must be replayable without side effects."

**Solution:** Implement idempotency using proven ADO pattern from GetSellDecisionsAsync:
- HasReportBeenSentAsync: SELECT COUNT from recommendation_sent_log
- MarkReportSentAsync: CREATE TABLE IF NOT EXISTS + INSERT with ON CONFLICT

**Changes:**
- RecommendationReportGenerator: Restored real idempotency logic (ADO pattern, no Dapper)
- GenerateDailyRecommendationJob: Restore idempotency check/mark calls
- GenerateWeeklyRecommendationJob: Restore idempotency check/mark calls
- GenerateMonthlyRecommendationJob: Restore idempotency check/mark calls

**Guarantees Restored:**
- Partial failure safe (Telegram succeeds, job throws → no duplicate on retry)
- Manual trigger safe (dashboard re-run → skips if already sent)
- [DisableConcurrentExecution] per CLAUDE.md blocking rule

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

src/KArtSell.Host/Jobs/GenerateDailyRecommendationJob.cs

@@ -38,8 +38,16 @@ public sealed class GenerateDailyRecommendationJob
             var now = _clock.UtcNow;
             var reportDate = now.DateTime.Date;
 
+            var idempotencyKey = $"daily:{reportDate:yyyy-MM-dd}";
+            if (await reportGenerator.HasReportBeenSentAsync(idempotencyKey, cancellationToken))
+            {
+                _logger.LogInformation("Daily report already sent for {Date}. Skipping", reportDate);
+                return;
+            }
+
             var report = await reportGenerator.GenerateDailyRecommendationAsync(reportDate, cancellationToken);
             await reportGenerator.SendRecommendationReportAsync(report, cancellationToken);
+            await reportGenerator.MarkReportSentAsync(idempotencyKey, cancellationToken);
 
             _logger.LogInformation(
                 "Daily recommendation report sent. Date={Date}, Recommendations={Count}",