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__/pty-run.test.js

@@ -398,6 +398,27 @@ describe("pty-run", () => {
     assert.ok(!call.some((a) => String(a).startsWith("--dangerously-bypass")));
   });
 
+  it("spawnRun runs `agy` for an antigravity lane, dropping flags it has no use for", () => {
+    const call = captureNewSession(() =>
+      pty.spawnRun({
+        laneId: 13,
+        cwd: "/tmp/repo",
+        tool: "antigravity",
+        model: "opus",
+        effort: "high",
+        permissionMode: "bypassPermissions",
+        initialPrompt: "hello",
+      })
+    );
+    assert.deepEqual(paneArgv(call), ["agy", "-i", "hello"]);
+
+    tmux.__reset();
+    const last = captureNewSession(() =>
+      pty.spawnRun({ laneId: 14, cwd: "/tmp/repo", tool: "antigravity", resumeLast: true })
+    );
+    assert.deepEqual(paneArgv(last), ["agy", "--continue"]);
+  });
+
   // `dashboard_runs.mode` is NOT NULL and recordRun swallows insert errors, so a
   // null there persisted nothing at all while every call still looked fine: the
   // runs modal rendered a row with no cwd, model, prompt or start time, and a