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/__tests__/lane-lifecycle.test.js

@@ -1302,4 +1302,20 @@ describe("lane ensure, start mode, lane_id and releasing a finished run", () =>
       restorePath();
     }
   });
+
+  it("healAllRunIds releases a lane whose pane exited, with no read to trigger it", async () => {
+    // A codex/antigravity pane fires no hook on exit, so nothing re-reads its
+    // lane; the server's periodic sweep is what has to notice.
+    const lanesLib = require("../lib/lanes");
+    const { healAllRunIds } = require("../routes/lanes");
+    const lane = await adoptedLane("heal-all-sweep");
+    // No tmux session by this name exists on the suite's private server.
+    lanesLib.updateLane(lane.id, { run_id: `agenthub-lane-${lane.id}`, status: "running" });
+
+    healAllRunIds();
+
+    const after = lanesLib.getLane(lane.id);
+    assert.equal(after.run_id, null);
+    assert.equal(after.status, "idle");
+  });
 });