Implement town activity logging (gt-ewzon)

Add centralized logging for Gas Town agent lifecycle events:
- spawn: new agent created
- wake: agent resumed
- nudge: message injected
- handoff: agent handed off
- done: agent finished work
- crash: agent exited unexpectedly
- kill: agent killed intentionally

Implementation:
- Add internal/townlog package with LogEvent() function
- Log to ~/gt/logs/town.log with human-readable format
- Add gt log command to view/tail/filter logs
- Integrate logging into spawn, nudge, handoff, done, stop, session commands

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

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

internal/cmd/handoff.go

@@ -11,6 +11,7 @@ import (
 	"github.com/steveyegge/gastown/internal/style"
 	"github.com/steveyegge/gastown/internal/tmux"
 	"github.com/steveyegge/gastown/internal/wisp"
+	"github.com/steveyegge/gastown/internal/workspace"
 )
 
 var handoffCmd = &cobra.Command{
@@ -126,6 +127,15 @@ func runHandoff(cmd *cobra.Command, args []string) error {
 	// Handing off ourselves - print feedback then respawn
 	fmt.Printf("%s Handing off %s...\n", style.Bold.Render("🤝"), currentSession)
 
+	// Log handoff event
+	if townRoot, err := workspace.FindFromCwd(); err == nil && townRoot != "" {
+		agent := sessionToGTRole(currentSession)
+		if agent == "" {
+			agent = currentSession
+		}
+		LogHandoff(townRoot, agent, handoffSubject)
+	}
+
 	// Dry run mode - show what would happen (BEFORE any side effects)
 	if handoffDryRun {
 		if handoffSubject != "" || handoffMessage != "" {