fix(codex): add multi-platform CLI discovery and static gpt-5.5 template fallback (#3382)

* fix(codex): add multi-platform CLI discovery and static gpt-5.5 template fallback for model catalog generation

When cc-switch generates a Codex model catalog for third-party providers,
it needs the gpt-5.5 model definition as a template. Previously it relied
on either ~/.codex/models_cache.json (only exists when Codex has connected
to OpenAI) or running 'codex debug models --bundled' (fails when codex
is not on the Tauri app's PATH, common in macOS GUI environments).

This commit adds a three-tier fallback:
1. Try 'codex' from PATH, then platform-specific common paths
   (/opt/homebrew/bin/codex, /usr/local/bin/codex, etc.)
2. If all CLI attempts fail, use a compile-time embedded gpt-5.5
   template (extracted from codex 0.135.0 bundled models)

Also adds tests for the static template validity and CLI candidates.

* fix(codex): discover user node codex installs

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Co-authored-by: Jason <farion1231@gmail.com>