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-agents.test.js

@@ -116,15 +116,17 @@ describe("installAgents", () => {
     assert.ok(fs.existsSync(path.join(cwd, ".claude", "agents")));
   });
 
-  it("installs nothing for a codex lane — no .claude/agents/, no AGENTS.md", async () => {
-    const cwd = makeRepoDir();
-    const lane = lanesLib.createLane({ title: "cx", cwd, kind: "managed", tool: "codex" });
+  for (const tool of ["codex", "antigravity"]) {
+    it(`installs nothing for a ${tool} lane — no .claude/agents/, no AGENTS.md`, async () => {
+      const cwd = makeRepoDir();
+      const lane = lanesLib.createLane({ title: "cx", cwd, kind: "managed", tool });
 
-    const result = await installAgents(lane);
-    assert.deepEqual(result.installed, []);
-    assert.equal(fs.existsSync(path.join(cwd, ".claude", "agents")), false);
-    assert.equal(fs.existsSync(path.join(cwd, "AGENTS.md")), false);
-  });
+      const result = await installAgents(lane);
+      assert.deepEqual(result.installed, []);
+      assert.equal(fs.existsSync(path.join(cwd, ".claude", "agents")), false);
+      assert.equal(fs.existsSync(path.join(cwd, "AGENTS.md")), false);
+    });
+  }
 });
 
 describe("codex pipeline cleanup", () => {