feat: add --parent flag to bd list command (bd-yqhh)

Filters issues by parent issue ID using parent-child dependencies.

Example: bd list --parent=bd-xyz --status=open

Changes:
- Add ParentID field to IssueFilter type
- Add --parent flag to list command
- Forward parent filter through RPC
- Implement filtering in SQLite and memory storage

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

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

cmd/bd/list.go

@@ -148,6 +148,9 @@ var listCmd = &cobra.Command{
 		// Template filtering (beads-1ra)
 		includeTemplates, _ := cmd.Flags().GetBool("include-templates")
 
+		// Parent filtering (bd-yqhh)
+		parentID, _ := cmd.Flags().GetString("parent")
+
 		// Use global jsonOutput set by PersistentPreRun
 
 		// Normalize labels: trim, dedupe, remove empty
@@ -311,6 +314,11 @@ var listCmd = &cobra.Command{
 			filter.IsTemplate = &isTemplate
 		}
 
+		// Parent filtering (bd-yqhh): filter children by parent issue
+		if parentID != "" {
+			filter.ParentID = &parentID
+		}
+
 		// Check database freshness before reading (bd-2q6d, bd-c4rq)
 		// Skip check when using daemon (daemon auto-imports on staleness)
 		ctx := rootCtx
@@ -392,6 +400,9 @@ var listCmd = &cobra.Command{
 			// Template filtering (beads-1ra)
 			listArgs.IncludeTemplates = includeTemplates
 
+			// Parent filtering (bd-yqhh)
+			listArgs.ParentID = parentID
+
 			 resp, err := daemonClient.List(listArgs)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "Error: %v\n", err)
@@ -666,6 +677,9 @@ func init() {
 	// Template filtering (beads-1ra): exclude templates by default
 	listCmd.Flags().Bool("include-templates", false, "Include template molecules in output")
 
+	// Parent filtering (bd-yqhh): filter children by parent issue
+	listCmd.Flags().String("parent", "", "Filter by parent issue ID (shows children of specified issue)")
+
 	// Note: --json flag is defined as a persistent flag in main.go, not here
 	rootCmd.AddCommand(listCmd)
 }