fix(antigravity): add fail-fast on 429 rate limit

When Antigravity returns 429, throw immediately instead of waiting for the
server-provided retry delay (which can be 10+ minutes). This lets clawdbot
quickly rotate to another account.

This patch was previously in PR #454 but was accidentally removed in 0dbb569
when bumping to pi-ai 0.40.0. The upstream release did NOT include this fix.

Context: Antigravity rate limits cause pi-ai to sleep for the full retry
delay inside the request, blocking the thread. Clawdbot's timeout would
eventually fire, but waiting 10+ minutes is unacceptable UX.

Bundled with the empty error message filter since both handle 429 recovery.

package.json

@@ -171,7 +171,8 @@
     },
     "patchedDependencies": {
       "@mariozechner/pi-agent-core": "patches/@mariozechner__pi-agent-core.patch",
-      "@mariozechner/pi-coding-agent": "patches/@mariozechner__pi-coding-agent.patch"
+      "@mariozechner/pi-coding-agent": "patches/@mariozechner__pi-coding-agent.patch",
+      "@mariozechner/pi-ai": "patches/@mariozechner__pi-ai.patch"
     }
   },
   "vitest": {
@@ -209,6 +210,7 @@
   "patchedDependencies": {
     "@mariozechner/pi-agent-core": "patches/@mariozechner__pi-agent-core.patch",
     "@mariozechner/pi-coding-agent": "patches/@mariozechner__pi-coding-agent.patch",
+      "@mariozechner/pi-ai": "patches/@mariozechner__pi-ai.patch",
     "qrcode-terminal": "patches/qrcode-terminal.patch",
     "playwright-core@1.57.0": "patches/playwright-core@1.57.0.patch"
   }