feat(plugin): add settings.json with opusplan model (#264)

* 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

Author: darrenhinde

plugins/claude-code/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "oac",
   "description": "OpenAgentsControl — multi-agent orchestration for Claude Code. Context-aware development with skills, subagents, parallel execution, and automated code review.",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "author": {
     "name": "darrenhinde",
     "url": "https://github.com/darrenhinde"

plugins/claude-code/README.md

@@ -320,14 +320,29 @@ Stage 4: Execute with loaded context → No nested discovery needed
 
 ## 🔧 Configuration
 
-The plugin uses context files from the main OpenAgents Control repository.
+### Model: opusplan
+
+The plugin ships with `settings.json` at the plugin root:
+
+```json
+{
+  "model": "opusplan"
+}
+```
+
+`opusplan` uses **Opus for planning/orchestration** (the main agent) and **Sonnet for execution** (subagents). This matches OAC's plan-first workflow and gives you Opus-quality reasoning without paying Opus rates for every tool call.
+
+Subagents that need a lighter model override this at the agent level (e.g. `external-scout` uses `haiku`). The root setting only affects the main orchestrating agent.
+
+To reload after any settings change: `/reload-plugins` (no restart needed).
 
 ### Context Structure
 
 ```
 plugins/claude-code/
 ├── .claude-plugin/
 │   └── plugin.json              # Plugin metadata
+├── settings.json                # Model config: opusplan
 ├── agents/                      # Custom subagents (7 files)
 │   ├── task-manager.md
 │   ├── context-scout.md

plugins/claude-code/settings.json

@@ -0,0 +1,3 @@
+{
+  "model": "opusplan"
+}