[codex] Add mobile performance skills

[vb-openai]

Summary

• Add iOS ETTrace profiling and memgraph leak investigation skills to build-ios-apps.
• Add Android performance profiling guidance and helper scripts to test-android-apps.
• Update plugin manifests, agent surfaces, and README copy to expose the new performance workflows.

Validation

• git apply --check /Users/vb/Downloads/mobile-performance-skills.patch
• git diff --check
• jq empty plugins/build-ios-apps/.codex-plugin/plugin.json plugins/test-android-apps/.codex-plugin/plugin.json
• Ruby YAML parse for changed agents/openai.yaml files
• bash -n on added shell helpers
• Python syntax parse for added Python helpers