feat: Codex account rotation + fix rate-limit detection

- New codex-token-rotation module: rotates between multiple
  ~/.codex-accounts/{n}/auth.json on rate-limit
- Copies active account auth to session dir before each spawn
- Fix detectFallbackTrigger to match "usage limit" / "hit your limit"
- Fix streamed error detection: remove claude-only guard so codex
  rate-limit errors are caught even when output.status is "success"
- Add rotation in both task-scheduler and message-agent-executor

src/provider-fallback.ts

@@ -247,6 +247,8 @@ export function detectFallbackTrigger(
   if (
     lower.includes('429') ||
     lower.includes('rate limit') ||
+    lower.includes('usage limit') ||
+    lower.includes('hit your limit') ||
     lower.includes('too many requests') ||
     lower.includes('rate_limit')
   ) {