fix: increase image request timeout

[ningzimu]

Summary

• Increase the default Codex Images request timeout from 180 seconds to 600 seconds.
• Update the changelog entry for the timeout behavior change.
• Sync the local installed codex-gpt-image skill copy.

Verification

• python3 -m py_compile skills/codex-gpt-image/scripts/codex_gpt_image.py
• python3 /Users/ningzimu/.codex/skills/.system/skill-creator/scripts/quick_validate.py skills/codex-gpt-image
• python3 /Users/ningzimu/.codex/skills/.system/skill-creator/scripts/quick_validate.py /Users/ningzimu/.agents/skills/codex-gpt-image
• git diff --check
• Parser default check returned 600

Notes

• The CLI still allows explicit --timeout overrides.