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.

client/src/components/run/__tests__/LaneConsolePane.test.tsx

@@ -84,6 +84,7 @@ function baseProps() {
     binaryStatus: {
       claude: { found: true, path: "/usr/local/bin/claude" },
       codex: { found: true, path: "/usr/local/bin/codex" },
+      antigravity: { found: true, path: "/usr/local/bin/agy" },
     },
     cwdSuggestions: [],
     activeRuns: { items: [] },