feat(list): add --pinned and --no-pinned filter flags

Add ability to filter issues by their pinned status in bd list command.

- Add pinned column to issues table via migration 023
- Add Pinned field to Issue struct and IssueFilter
- Update all storage layer queries to include pinned column
- Add --pinned flag to show only pinned issues
- Add --no-pinned flag to exclude pinned issues
- Update RPC layer to forward pinned filter to daemon mode
- Add pinned to allowedUpdateFields for bd update support

Resolves: beads-p8e

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

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

internal/storage/sqlite/dependencies.go

@@ -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
+		// Pinned flag (bd-p8e)
+		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
 		}
+		// Pinned flag (bd-p8e)
+		if pinned.Valid && pinned.Int64 != 0 {
+			issue.Pinned = true
+		}
 
 		issues = append(issues, &issue)
 		issueIDs = append(issueIDs, issue.ID)