feat: Add created_by field to issues (GH#748)

Add a created_by field to track who created each issue, similar to how
comments have an author field.

- Add CreatedBy string field to Issue struct
- Add migration 029 to add created_by column to issues table
- Update all SELECT/INSERT/Scan statements across storage layer
- Populate created_by in bd create from actor chain
- Display created_by in bd show output

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

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

internal/storage/sqlite/transaction.go

@@ -310,7 +310,7 @@ func (t *sqliteTxStorage) GetIssue(ctx context.Context, id string) (*types.Issue
 	row := t.conn.QueryRowContext(ctx, `
 		SELECT id, content_hash, title, description, design, acceptance_criteria, notes,
 		       status, priority, issue_type, assignee, estimated_minutes,
-		       created_at, updated_at, closed_at, external_ref,
+		       created_at, created_by, updated_at, closed_at, external_ref,
 		       compaction_level, compacted_at, compacted_at_commit, original_size, source_repo, close_reason,
 		       deleted_at, deleted_by, delete_reason, original_type,
 		       sender, ephemeral, pinned, is_template,
@@ -1127,7 +1127,7 @@ func (t *sqliteTxStorage) SearchIssues(ctx context.Context, query string, filter
 	querySQL := fmt.Sprintf(`
 		SELECT id, content_hash, title, description, design, acceptance_criteria, notes,
 		       status, priority, issue_type, assignee, estimated_minutes,
-		       created_at, updated_at, closed_at, external_ref,
+		       created_at, created_by, updated_at, closed_at, external_ref,
 		       compaction_level, compacted_at, compacted_at_commit, original_size, source_repo, close_reason,
 		       deleted_at, deleted_by, delete_reason, original_type,
 		       sender, ephemeral, pinned, is_template,
@@ -1188,7 +1188,7 @@ func scanIssueRow(row scanner) (*types.Issue, error) {
 		&issue.ID, &contentHash, &issue.Title, &issue.Description, &issue.Design,
 		&issue.AcceptanceCriteria, &issue.Notes, &issue.Status,
 		&issue.Priority, &issue.IssueType, &assignee, &estimatedMinutes,
-		&issue.CreatedAt, &issue.UpdatedAt, &closedAt, &externalRef,
+		&issue.CreatedAt, &issue.CreatedBy, &issue.UpdatedAt, &closedAt, &externalRef,
 		&issue.CompactionLevel, &compactedAt, &compactedAtCommit, &originalSize, &sourceRepo, &closeReason,
 		&deletedAt, &deletedBy, &deleteReason, &originalType,
 		&sender, &wisp, &pinned, &isTemplate,