Instrument gt commands to emit events to activity feed (gt-7aw1m)

Add events.LogFeed calls to the following gt commands:
- nudge.go: Log TypeNudge events when nudging agents
- unsling.go: Log TypeUnhook events when removing work from hooks
- up.go: Log TypeBoot events when starting Gas Town services
- down.go: Log TypeHalt events when stopping Gas Town services
- stop.go: Log TypeKill events when stopping polecat sessions
- polecat_spawn.go: Log TypeSpawn events when spawning polecats

Also add helper functions to events package:
- UnhookPayload: Creates payload for unhook events
- KillPayload: Creates payload for kill events
- HaltPayload: Creates payload for halt events

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

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

internal/cmd/stop.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/spf13/cobra"
 	"github.com/steveyegge/gastown/internal/config"
+	"github.com/steveyegge/gastown/internal/events"
 	"github.com/steveyegge/gastown/internal/git"
 	"github.com/steveyegge/gastown/internal/rig"
 	"github.com/steveyegge/gastown/internal/session"
@@ -147,6 +148,9 @@ func runStop(cmd *cobra.Command, args []string) error {
 				logger := townlog.NewLogger(townRoot)
 				logger.Log(townlog.EventKill, agent, "gt stop")
 
+				// Log kill event to activity feed
+				_ = events.LogFeed(events.TypeKill, "gt", events.KillPayload(r.Name, info.Polecat, "gt stop"))
+
 				// Log captured output (truncated)
 				if len(output) > 200 {
 					output = output[len(output)-200:]