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/lib/dashboard-runs.js

@@ -89,7 +89,7 @@ function recordRun(handle) {
       started_at: startedAt,
       ended_at: endedAt,
       lane_id: typeof handle.laneId === "number" ? handle.laneId : null,
-      tool: handle.tool === "codex" ? "codex" : "claude",
+      tool: handle.tool === "codex" || handle.tool === "antigravity" ? handle.tool : "claude",
     });
   } catch (err) {
     // Best-effort by design (a live run must never fail because sqlite did),