Fix overflow E2E cleanup timeout

[selfcontained]

Summary

• seed overflow-only rows as terminal agents outside the repository
• avoid triggering Codex token harvesting and repository stop hooks during bulk cleanup
• retain all existing layout and scrolling assertions

Root cause

The 24 synthetic agents defaulted to type: "codex". The cleanup helper stops and archives each agent, and both lifecycle paths trigger Codex token harvesting. Each harvest recursively scans ~/.codex/sessions, so 24 concurrent synthetic agents caused enough duplicated filesystem work to delay DELETE responses until the 30-second afterAll timeout. The layout test does not exercise Codex sessions, token usage, worktrees, or repo hooks.

Validation

• pnpm run check
• pnpm run test:e2e e2e/overflow-layout.spec.ts --workers=1 — 2 passed in 3.9s
• pnpm run test:e2e — changed overflow tests passed; unrelated focused agent does not trigger notification SSE event was flaky
• focused rerun of the unrelated notification test — passed
• pnpm run test:e2e --project=serial --no-deps — 45 passed, 11 expected skips
• headless Playwright overflow interaction and screenshot