docs(agents): correct stale test count

[alex-mextner]

Summary

• Update AGENTS.md test-count guidance from stale ~578 to the exact 1010 pass count observed from bun test.

Verification

• bun test (reports 1010 pass, 4 fail, 3107 expect() calls, 1014 tests across 70 files)
• Failures observed on origin/main baseline in this sandbox: 3 Chrome print-to-pdf integration failures and 1 codex ancestor model-detection test.