* feat(plugin): add settings.json with opusplan model for Claude Code plugin
Adds plugins/claude-code/settings.json with { "model": "opusplan" } so
the OAC plugin automatically uses Opus for planning/orchestration and
Sonnet for subagent execution — matching OAC's plan-first workflow.
Plugin-scoped settings.json takes priority over global/user settings
when the plugin is loaded (marketplace install or --plugin-dir).
Subagents that need a lighter model continue to override at the agent
level (external-scout → haiku, task-manager/test-engineer/coder-agent → sonnet).
Closes#35
* chore(plugin): bump version to 1.0.2 for marketplace pickup
