feat(bd): add 'bd types' command to list valid issue types

Lists all valid issue types with descriptions, organized by category:
- Work types (task, bug, feature, chore, epic)
- System types (molecule, gate, convoy, merge-request, slot)
- Agent types (agent, role, rig, event, message)

Supports --json output for scripting.

Closes: bd-9ilm5

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

cmd/bd/types.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/beads/internal/types"
+)
+
+// AllIssueTypes returns all valid built-in issue types with descriptions.
+// Ordered by typical usage frequency: work types first, then system types.
+var allIssueTypes = []struct {
+	Type        types.IssueType
+	Description string
+}{
+	// Work types (common user-facing types)
+	{types.TypeTask, "General work item (default)"},
+	{types.TypeBug, "Bug report or defect"},
+	{types.TypeFeature, "New feature or enhancement"},
+	{types.TypeChore, "Maintenance or housekeeping"},
+	{types.TypeEpic, "Large body of work spanning multiple issues"},
+
+	// System types (used by tooling)
+	{types.TypeMolecule, "Template for issue hierarchies"},
+	{types.TypeGate, "Async coordination gate"},
+	{types.TypeConvoy, "Cross-project tracking with reactive completion"},
+	{types.TypeMergeRequest, "Merge queue entry for refinery processing"},
+	{types.TypeSlot, "Exclusive access slot (merge-slot gate)"},
+
+	// Agent types (Gas Town infrastructure)
+	{types.TypeAgent, "Agent identity bead"},
+	{types.TypeRole, "Agent role definition"},
+	{types.TypeRig, "Rig identity bead (multi-repo workspace)"},
+	{types.TypeEvent, "Operational state change record"},
+	{types.TypeMessage, "Ephemeral communication between workers"},
+}
+
+var typesCmd = &cobra.Command{
+	Use:     "types",
+	GroupID: "views",
+	Short:   "List valid issue types",
+	Long: `List all valid issue types that can be used with bd create --type.
+
+Types are organized into categories:
+- Work types: Common types for tracking work (task, bug, feature, etc.)
+- System types: Used by beads tooling (molecule, gate, convoy, etc.)
+- Agent types: Used by Gas Town agent infrastructure
+
+Examples:
+  bd types              # List all types with descriptions
+  bd types --json       # Output as JSON
+`,
+	Run: func(cmd *cobra.Command, args []string) {
+		if jsonOutput {
+			result := struct {
+				Types []struct {
+					Name        string `json:"name"`
+					Description string `json:"description"`
+				} `json:"types"`
+			}{}
+
+			for _, t := range allIssueTypes {
+				result.Types = append(result.Types, struct {
+					Name        string `json:"name"`
+					Description string `json:"description"`
+				}{
+					Name:        string(t.Type),
+					Description: t.Description,
+				})
+			}
+			outputJSON(result)
+			return
+		}
+
+		// Text output with categories
+		fmt.Println("Work types:")
+		for _, t := range allIssueTypes[:5] {
+			fmt.Printf("  %-14s %s\n", t.Type, t.Description)
+		}
+
+		fmt.Println("\nSystem types:")
+		for _, t := range allIssueTypes[5:10] {
+			fmt.Printf("  %-14s %s\n", t.Type, t.Description)
+		}
+
+		fmt.Println("\nAgent types:")
+		for _, t := range allIssueTypes[10:] {
+			fmt.Printf("  %-14s %s\n", t.Type, t.Description)
+		}
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(typesCmd)
+}