feat(lanes): add lane tools menu and header liveness/age indicator

Move the rare destructive lane actions behind a LaneToolsMenu next to
the lane header, and show a liveness dot + status label + stage age
inline in the header instead of only in the card grid.

client/src/i18n/locales/en/lanes.json

@@ -1,6 +1,6 @@
 {
   "action.clear": "clear state",
-  "action.forget": "delete lane",
+  "action.forget": "Delete lane",
   "action.purge": "delete history",
   "action.remove": "delete lane + worktree",
   "action.reset": "reset worktree",
@@ -16,6 +16,7 @@
   "actions.syncCheck": "Check dev sync",
   "actions.syncCheckClean": "DEV_DELTA: {{count}} file(s), overlap: {{overlap}}",
   "actions.syncCheckCollision": "Migration collision: {{file}} → rename to {{suggestion}}",
+  "actions.tools": "Tools",
   "add": "Add lane",
   "addLane": "Create a lane from a working directory",
   "addLaneBaseLabel": "Branch to fork from",