feat(identity): add gt commit wrapper and gt trail command

gt-f6mkz: Agent git identity
- Add `gt commit` wrapper that sets git author from agent identity
- Identity mapping: gastown/crew/jack → gastown.crew.jack@gastown.local
- Add `agent_email_domain` to TownSettings (default: gastown.local)
- Add `gt config agent-email-domain` command to manage domain

gt-j1m5v: gt trail command
- Add `gt trail` with aliases `gt recent` and `gt recap`
- Subcommands: commits, beads, hooks
- Flags: --since, --limit, --json, --all
- Filter commits by agent email domain

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

internal/cmd/commit_test.go

@@ -0,0 +1,71 @@
+package cmd
+
+import "testing"
+
+func TestIdentityToEmail(t *testing.T) {
+	tests := []struct {
+		name     string
+		identity string
+		domain   string
+		want     string
+	}{
+		{
+			name:     "crew member",
+			identity: "gastown/crew/jack",
+			domain:   "gastown.local",
+			want:     "gastown.crew.jack@gastown.local",
+		},
+		{
+			name:     "polecat",
+			identity: "gastown/polecats/max",
+			domain:   "gastown.local",
+			want:     "gastown.polecats.max@gastown.local",
+		},
+		{
+			name:     "witness",
+			identity: "gastown/witness",
+			domain:   "gastown.local",
+			want:     "gastown.witness@gastown.local",
+		},
+		{
+			name:     "refinery",
+			identity: "gastown/refinery",
+			domain:   "gastown.local",
+			want:     "gastown.refinery@gastown.local",
+		},
+		{
+			name:     "mayor with trailing slash",
+			identity: "mayor/",
+			domain:   "gastown.local",
+			want:     "mayor@gastown.local",
+		},
+		{
+			name:     "deacon with trailing slash",
+			identity: "deacon/",
+			domain:   "gastown.local",
+			want:     "deacon@gastown.local",
+		},
+		{
+			name:     "custom domain",
+			identity: "myrig/crew/alice",
+			domain:   "example.com",
+			want:     "myrig.crew.alice@example.com",
+		},
+		{
+			name:     "deeply nested",
+			identity: "rig/polecats/nested/deep",
+			domain:   "test.io",
+			want:     "rig.polecats.nested.deep@test.io",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := identityToEmail(tt.identity, tt.domain)
+			if got != tt.want {
+				t.Errorf("identityToEmail(%q, %q) = %q, want %q",
+					tt.identity, tt.domain, got, tt.want)
+			}
+		})
+	}
+}