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/config/types.go

@@ -56,6 +56,11 @@ type TownSettings struct {
 	// This allows cost optimization by using different models for different roles.
 	// Example: {"mayor": "claude-opus", "witness": "claude-haiku", "polecat": "claude-sonnet"}
 	RoleAgents map[string]string `json:"role_agents,omitempty"`
+
+	// AgentEmailDomain is the domain used for agent git identity emails.
+	// Agent addresses like "gastown/crew/jack" become "gastown.crew.jack@{domain}".
+	// Default: "gastown.local"
+	AgentEmailDomain string `json:"agent_email_domain,omitempty"`
 }
 
 // NewTownSettings creates a new TownSettings with defaults.