Fix Codex CLI compatibility with current config behavior

[BorisEagle]

This updates the Codex CLI integration to work with current Codex behavior.

Observed failures:

1. qqqa passed:
   -c "tools.web_search=false"

   Codex rejected this with:
   invalid type: boolean false, expected struct WebSearchToolConfig
   in tools.web_search

2. After removing that override, qqqa still passed:
   -c "model_reasoning_effort=minimal"

   Codex then rejected the request because web_search could not be used with reasoning effort minimal.

Changes in this PR:

• remove the stale tools.web_search=false override
• change the default reasoning effort from minimal to low

This restored compatibility with the current Codex CLI provider flow for me.

[iagooar]

Superseded by #50, which also updates the bundled codex profile default (your patch only changed the CLI fallback). Thanks!

[iagooar]

Merged via #50. Thanks @BorisEagle!