feat(migration): Add gt migrate-agents command for two-level architecture (gt-nnub1)

Implements Phase 4 of the two-level beads architecture migration:
- Add hq- prefix helper functions for town-level agent beads
- Add CreateWithID method for deterministic bead creation
- Create gt migrate-agents command with dry-run/execute modes
- Migrate gt-mayor/gt-deacon to hq-mayor/hq-deacon in town beads
- Migrate role beads (gt-*-role) to town beads (hq-*-role)
- Add migration labels to old beads for tracking
- Idempotent: skips already-migrated beads

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

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

internal/cmd/migrate_agents_test.go

@@ -0,0 +1,95 @@
+package cmd
+
+import (
+	"testing"
+
+	"github.com/steveyegge/gastown/internal/beads"
+)
+
+func TestMigrationResultStatus(t *testing.T) {
+	tests := []struct {
+		name     string
+		result   migrationResult
+		wantIcon string
+	}{
+		{
+			name: "migrated shows checkmark",
+			result: migrationResult{
+				OldID:   "gt-mayor",
+				NewID:   "hq-mayor",
+				Status:  "migrated",
+				Message: "successfully migrated",
+			},
+			wantIcon: "✓",
+		},
+		{
+			name: "would migrate shows checkmark",
+			result: migrationResult{
+				OldID:   "gt-mayor",
+				NewID:   "hq-mayor",
+				Status:  "would migrate",
+				Message: "would copy state from gt-mayor",
+			},
+			wantIcon: "✓",
+		},
+		{
+			name: "skipped shows empty circle",
+			result: migrationResult{
+				OldID:   "gt-mayor",
+				NewID:   "hq-mayor",
+				Status:  "skipped",
+				Message: "already exists",
+			},
+			wantIcon: "⊘",
+		},
+		{
+			name: "error shows X",
+			result: migrationResult{
+				OldID:   "gt-mayor",
+				NewID:   "hq-mayor",
+				Status:  "error",
+				Message: "failed to create",
+			},
+			wantIcon: "✗",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var icon string
+			switch tt.result.Status {
+			case "migrated", "would migrate":
+				icon = "✓"
+			case "skipped":
+				icon = "⊘"
+			case "error":
+				icon = "✗"
+			}
+			if icon != tt.wantIcon {
+				t.Errorf("icon for status %q = %q, want %q", tt.result.Status, icon, tt.wantIcon)
+			}
+		})
+	}
+}
+
+func TestTownBeadIDHelpers(t *testing.T) {
+	tests := []struct {
+		name string
+		got  string
+		want string
+	}{
+		{"MayorBeadIDTown", beads.MayorBeadIDTown(), "hq-mayor"},
+		{"DeaconBeadIDTown", beads.DeaconBeadIDTown(), "hq-deacon"},
+		{"DogBeadIDTown", beads.DogBeadIDTown("fido"), "hq-dog-fido"},
+		{"RoleBeadIDTown mayor", beads.RoleBeadIDTown("mayor"), "hq-mayor-role"},
+		{"RoleBeadIDTown witness", beads.RoleBeadIDTown("witness"), "hq-witness-role"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.got != tt.want {
+				t.Errorf("%s = %q, want %q", tt.name, tt.got, tt.want)
+			}
+		})
+	}
+}