feat(cleanup): protect pinned issues from cleanup/compact (bd-b2k)

Add Pinned field to Issue struct and database schema to protect
issues from accidental deletion via cleanup or compaction.

Changes:
- Add Pinned bool field to types.Issue
- Create migration 023_pinned_column.go for database schema
- Filter out pinned issues in cleanup command before deletion
- Add pinned check to GetTier1Candidates and GetTier2Candidates
- Add pinned check to CheckEligibility for compaction
- Update all SQL queries and scan functions to include pinned field

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/storage/sqlite/dependencies.go

@@ -233,7 +233,7 @@ func (s *SQLiteStorage) GetDependenciesWithMetadata(ctx context.Context, issueID
 		       i.status, i.priority, i.issue_type, i.assignee, i.estimated_minutes,
 		       i.created_at, i.updated_at, i.closed_at, i.external_ref, i.source_repo,
 		       i.deleted_at, i.deleted_by, i.delete_reason, i.original_type,
-		       i.sender, i.ephemeral,
+		       i.sender, i.ephemeral, i.pinned,
 		       d.type
 		FROM issues i
 		JOIN dependencies d ON i.id = d.depends_on_id
@@ -255,7 +255,7 @@ func (s *SQLiteStorage) GetDependentsWithMetadata(ctx context.Context, issueID s
 		       i.status, i.priority, i.issue_type, i.assignee, i.estimated_minutes,
 		       i.created_at, i.updated_at, i.closed_at, i.external_ref, i.source_repo,
 		       i.deleted_at, i.deleted_by, i.delete_reason, i.original_type,
-		       i.sender, i.ephemeral,
+		       i.sender, i.ephemeral, i.pinned,
 		       d.type
 		FROM issues i
 		JOIN dependencies d ON i.id = d.issue_id
@@ -714,6 +714,8 @@ func (s *SQLiteStorage) scanIssues(ctx context.Context, rows *sql.Rows) ([]*type
 		// Messaging fields (bd-kwro)
 		var sender sql.NullString
 		var ephemeral sql.NullInt64
+		// Protection fields (bd-b2k)
+		var pinned sql.NullInt64
 
 		err := rows.Scan(
 			&issue.ID, &contentHash, &issue.Title, &issue.Description, &issue.Design,
@@ -721,7 +723,7 @@ func (s *SQLiteStorage) scanIssues(ctx context.Context, rows *sql.Rows) ([]*type
 			&issue.Priority, &issue.IssueType, &assignee, &estimatedMinutes,
 			&issue.CreatedAt, &issue.UpdatedAt, &closedAt, &externalRef, &sourceRepo, &closeReason,
 			&deletedAt, &deletedBy, &deleteReason, &originalType,
-			&sender, &ephemeral,
+			&sender, &ephemeral, &pinned,
 		)
 		if err != nil {
 			return nil, fmt.Errorf("failed to scan issue: %w", err)
@@ -766,6 +768,10 @@ func (s *SQLiteStorage) scanIssues(ctx context.Context, rows *sql.Rows) ([]*type
 		if ephemeral.Valid && ephemeral.Int64 != 0 {
 			issue.Ephemeral = true
 		}
+		// Protection fields (bd-b2k)
+		if pinned.Valid && pinned.Int64 != 0 {
+			issue.Pinned = true
+		}
 
 		issues = append(issues, &issue)
 		issueIDs = append(issueIDs, issue.ID)
@@ -805,6 +811,8 @@ func (s *SQLiteStorage) scanIssuesWithDependencyType(ctx context.Context, rows *
 		// Messaging fields (bd-kwro)
 		var sender sql.NullString
 		var ephemeral sql.NullInt64
+		// Protection fields (bd-b2k)
+		var pinned sql.NullInt64
 		var depType types.DependencyType
 
 		err := rows.Scan(
@@ -813,7 +821,7 @@ func (s *SQLiteStorage) scanIssuesWithDependencyType(ctx context.Context, rows *
 			&issue.Priority, &issue.IssueType, &assignee, &estimatedMinutes,
 			&issue.CreatedAt, &issue.UpdatedAt, &closedAt, &externalRef, &sourceRepo,
 			&deletedAt, &deletedBy, &deleteReason, &originalType,
-			&sender, &ephemeral,
+			&sender, &ephemeral, &pinned,
 			&depType,
 		)
 		if err != nil {
@@ -856,6 +864,10 @@ func (s *SQLiteStorage) scanIssuesWithDependencyType(ctx context.Context, rows *
 		if ephemeral.Valid && ephemeral.Int64 != 0 {
 			issue.Ephemeral = true
 		}
+		// Protection fields (bd-b2k)
+		if pinned.Valid && pinned.Int64 != 0 {
+			issue.Pinned = true
+		}
 
 		// Fetch labels for this issue
 		labels, err := s.GetLabels(ctx, issue.ID)