fix: Mark dependent issues dirty when deleting to prevent orphan deps in JSONL

When an issue is deleted, issues that depend on it were not being marked
dirty. This caused stale dependency references to persist in JSONL after
the target issue was deleted, because the dependent issues were never
re-exported.

This manifests as FK validation failures during multi-repo hydration:
"foreign key violation: issue X depends on non-existent issue Y"

The fix queries for dependent issues before deleting and marks them dirty
so they get re-exported without the stale dependency reference.

Adds test: TestDeleteIssueMarksDependentsDirty

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

internal/storage/sqlite/queries.go

@@ -1343,6 +1343,32 @@ func (s *SQLiteStorage) DeleteIssue(ctx context.Context, id string) error {
 	}
 	defer func() { _ = tx.Rollback() }()
 
+	// Mark issues that depend on this one as dirty so they get re-exported
+	// without the stale dependency reference (fixes orphan deps in JSONL)
+	rows, err := tx.QueryContext(ctx, `SELECT issue_id FROM dependencies WHERE depends_on_id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("failed to query dependent issues: %w", err)
+	}
+	var dependentIDs []string
+	for rows.Next() {
+		var depID string
+		if err := rows.Scan(&depID); err != nil {
+			_ = rows.Close()
+			return fmt.Errorf("failed to scan dependent issue ID: %w", err)
+		}
+		dependentIDs = append(dependentIDs, depID)
+	}
+	_ = rows.Close()
+	if err := rows.Err(); err != nil {
+		return fmt.Errorf("failed to iterate dependent issues: %w", err)
+	}
+
+	if len(dependentIDs) > 0 {
+		if err := markIssuesDirtyTx(ctx, tx, dependentIDs); err != nil {
+			return fmt.Errorf("failed to mark dependent issues dirty: %w", err)
+		}
+	}
+
 	// Delete dependencies (both directions)
 	_, err = tx.ExecContext(ctx, `DELETE FROM dependencies WHERE issue_id = ? OR depends_on_id = ?`, id, id)
 	if err != nil {