feat: Add crew session cycling fix and daemon exponential backoff (gt-ws8ol)

- Fix crew next/prev: Pass session name via key binding to avoid run-shell context issue
- Add TouchTownActivity() for town-level activity signaling
- Implement daemon exponential backoff based on activity.json:
  - 0-5 min idle → 5 min heartbeat
  - 5-15 min idle → 10 min heartbeat
  - 15-45 min idle → 30 min heartbeat
  - 45+ min idle → 60 min heartbeat (max)

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

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

internal/keepalive/keepalive.go

@@ -64,6 +64,69 @@ func TouchInWorkspace(workspaceRoot, command string) {
 	_ = os.WriteFile(keepalivePath, data, 0644) // non-fatal: status file for debugging
 }
 
+// TouchTownActivity writes a town-level activity signal to ~/gt/daemon/activity.json.
+// This is used by the daemon to implement exponential backoff when the town is idle.
+// Any gt command activity resets the backoff to the base heartbeat interval.
+// It silently ignores errors (best-effort signaling).
+func TouchTownActivity(command string) {
+	// Get town root from GT_TOWN_ROOT or default to ~/gt
+	townRoot := os.Getenv("GT_TOWN_ROOT")
+	if townRoot == "" {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return
+		}
+		townRoot = filepath.Join(home, "gt")
+	}
+
+	daemonDir := filepath.Join(townRoot, "daemon")
+
+	// Ensure daemon directory exists
+	if err := os.MkdirAll(daemonDir, 0755); err != nil {
+		return
+	}
+
+	state := State{
+		LastCommand: command,
+		Timestamp:   time.Now().UTC(),
+	}
+
+	data, err := json.Marshal(state)
+	if err != nil {
+		return
+	}
+
+	activityPath := filepath.Join(daemonDir, "activity.json")
+	_ = os.WriteFile(activityPath, data, 0644) // non-fatal: activity signal for daemon
+}
+
+// ReadTownActivity returns the current town-level activity state.
+// Returns nil if the file doesn't exist or can't be read.
+func ReadTownActivity() *State {
+	townRoot := os.Getenv("GT_TOWN_ROOT")
+	if townRoot == "" {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return nil
+		}
+		townRoot = filepath.Join(home, "gt")
+	}
+
+	activityPath := filepath.Join(townRoot, "daemon", "activity.json")
+
+	data, err := os.ReadFile(activityPath)
+	if err != nil {
+		return nil
+	}
+
+	var state State
+	if err := json.Unmarshal(data, &state); err != nil {
+		return nil
+	}
+
+	return &state
+}
+
 // Read returns the current keepalive state for the workspace.
 // Returns nil if the file doesn't exist or can't be read.
 func Read(workspaceRoot string) *State {