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/unsling.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/spf13/cobra"
 	"github.com/steveyegge/gastown/internal/beads"
+	"github.com/steveyegge/gastown/internal/events"
 	"github.com/steveyegge/gastown/internal/style"
 )
 
@@ -141,6 +142,9 @@ func runUnsling(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("unpinning bead %s: %w", pinned.ID, err)
 	}
 
+	// Log unhook event
+	_ = events.LogFeed(events.TypeUnhook, agentID, events.UnhookPayload(pinned.ID))
+
 	fmt.Printf("%s Work removed from hook\n", style.Bold.Render("✓"))
 	fmt.Printf("  Bead %s is now status=open\n", pinned.ID)