fix(storage): use strict INSERT for batch issue creation (GH#956)

Add insertIssuesStrict function that uses plain INSERT instead of
INSERT OR IGNORE. Update bulkInsertIssues and transactional CreateIssues
to use the strict variant.

This fixes a race condition where INSERT OR IGNORE could silently skip
duplicate insertions, but the code would still attempt to record events
for those "inserted" issues, causing FOREIGN KEY constraint failures.

The strict INSERT will now fail explicitly if a duplicate is encountered,
which should never happen since checkForExistingIDs runs first within
the same transaction.

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

internal/storage/sqlite/transaction.go

@@ -297,14 +297,15 @@ func (t *sqliteTxStorage) CreateIssues(ctx context.Context, issues []*types.Issu
 	}
 
 	// GH#956: Check for conflicts with existing IDs in database before inserting.
-	// This prevents INSERT OR IGNORE from silently skipping duplicates, which would
-	// cause FK constraint failures when recording events for non-inserted issues.
+	// This prevents duplicates from causing FK constraint failures when recording events.
 	if err := checkForExistingIDs(ctx, t.conn, issues); err != nil {
 		return err
 	}
 
-	// Insert all issues
-	if err := insertIssues(ctx, t.conn, issues); err != nil {
+	// Insert all issues using strict mode (fails on duplicates)
+	// GH#956: Use insertIssuesStrict instead of insertIssues to prevent FK constraint errors
+	// from silent INSERT OR IGNORE failures under concurrent load.
+	if err := insertIssuesStrict(ctx, t.conn, issues); err != nil {
 		return fmt.Errorf("failed to insert issues: %w", err)
 	}