fix(codex-runtime): reapply migration when already enabled

[aqilaziz]

Fixes #26529

Summary

• allow /codex-runtime codex_app_server to re-run the Codex config migration when model.openai_runtime is already codex_app_server
• keep the auto no-op path unchanged
• skip config persistence on reapply while still running the idempotent MCP/plugin migration
• add a regression test covering the reapply path

Tests

• python -m pytest -o addopts='' tests\hermes_cli\test_codex_runtime_switch.py -q --tb=short
• python -m py_compile hermes_cli\codex_runtime_switch.py tests\hermes_cli\test_codex_runtime_switch.py
• python -m ruff check hermes_cli\codex_runtime_switch.py tests\hermes_cli\test_codex_runtime_switch.py
• git diff --check

[alt-glitch]

Competing fix: #26532 by @simpolism (issue author) targets the same bug with the same approach. Both modify codex_runtime_switch.py identically in logic. Maintainer should pick one.

[aqilaziz]

Thanks for flagging. I’m fine with maintainers taking #26532 if they prefer the issue-author branch; this PR can serve as an alternate or be closed if #26532 lands first.