fix: remove opencode-openai-codex-auth plugin from repo config

The plugin was causing CI runner failures because bundled bun binaries
cannot dynamically import external modules. This plugin is for local
dev use and should be in user's global config instead.

Author: shuv1337

.opencode/opencode.jsonc

@@ -1,6 +1,5 @@
 {
   "$schema": "https://opencode.ai/config.json",
-  "plugin": ["opencode-openai-codex-auth"],
   // "enterprise": {
   //   "url": "https://enterprise.dev.opencode.ai",
   // },