fix(agent): handle Codex stdin EOF status

[simfor99]

What Changed

• Prevent Codex agent runs from waiting on inherited stdin by supplying EOF, while accepting its informational stdin status output.
• Add coverage for the Codex EOF path and isolate hook-based git tests from global hook configuration.

Risk Assessment

✅ Low: Die Änderung ergänzt nur einen korrekten Hinweis und einen begrenzten Regressionstest für das bereits bestehende EOF-Verhalten von cmd.Stdin = nil.

Testing

Completed 1 recorded test check.

• Outcome: 🔧 1 issue found → auto-fixed ✅ across 2 runs (11m32s)

Pipeline

Updates from git push no-mistakes

⏭️ **intent** - skipped

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

✅ **Review** - passed

✅ No issues found.

🔧 **Test** - 1 issue found → auto-fixed ✅

• 🚨 tests failed with exit code 1
• go test -race ./...

🔧 Fix: test: isolate hooks from global config
✅ Re-checked - no issues remain.

• go test -race ./...

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.