Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

This recent PR #8093 added env flag to disable loading project config, but it would also be very useful to do the opposite - disable GLOBAL config loading.

Use Case

Creating project agent configurations - global config messes with local configuration.

Usage

OPENCODE_DISABLE_GLOBAL_CONFIG=true opencode - will load project config but ignore global.

PR with implementation: #10013