feat(lanes): Antigravity lanes, release exited panes, fresh Codex starts

- antigravity: a third lane tool running Antigravity's `agy` CLI. `-i`
  carries the first prompt, `--continue` resumes; `agy` has no model,
  effort or permission flag, and `--dangerously-skip-permissions` is never
  emitted. No pipeline, no agents install, and no AI Router (native only,
  else EUNSUPPORTED). Add lane gains an Antigravity choice and the binary
  probe maps it to `agy`.
- UI: the lane card no longer renders a frame holding only a "Codex" chip,
  and the prompt box names the lane's CLI ("Ask Codex anything…"), via
  LANE_TOOL_LABEL.
- runs: a pane that exits is released on a 10 s server beat
  (healAllRunIds, DASHBOARD_RUN_HEAL_MS). Codex and Antigravity fire no
  hook, so their lanes stayed "running" until something re-read them.
- codex: Start no longer sends resumeLast — only "Resume last session"
  continues the previous thread.

server/routes/lanes.js

@@ -106,6 +106,16 @@ function healRunId(lane) {
   return lanesLib.getLane(lane.id);
 }
 
+/**
+ * Heal every lane at once. A claude pane that exits fires a hook, which
+ * broadcasts the lane and so re-reads it; a codex or antigravity pane fires
+ * nothing, so without this sweep its lane read "running" until something
+ * else happened to fetch it.
+ */
+function healAllRunIds() {
+  for (const lane of lanesLib.listLanes()) if (lane.run_id) healRunId(lane);
+}
+
 function payload(lane) {
   const healed = healRunId(lane);
   return lanesLib.lanePayload(healed, lastEventAge(healed));
@@ -697,7 +707,8 @@ router.post("/:id/router/apply", sameOriginGuard, (req, res) => {
     broadcastLane(lane.id);
     res.json({ ...result, restart_required: live, run_id: live ? runId : null });
   } catch (err) {
-    const status = { ENOTFOUND: 404, EBADJSON: 409, EBADNAME: 400 }[err.code] || 500;
+    const status =
+      { ENOTFOUND: 404, EBADJSON: 409, EBADNAME: 400, EUNSUPPORTED: 400 }[err.code] || 500;
     res.status(status).json({ error: { code: err.code || "ERUNTIME", message: err.message } });
   }
 });
@@ -1777,3 +1788,4 @@ router.delete("/:id", sameOriginGuard, (req, res) => {
 
 module.exports = router;
 module.exports.broadcastLane = broadcastLane;
+module.exports.healAllRunIds = healAllRunIds;