improvement: add settings.json default agent to plugin package

[Luis85]

Context

Part of the plugin audit in #444 (§2, R5). Adopters who install Specorator as a plugin currently get raw Claude Code — no default agent is declared in the plugin package. Setting orchestrator as the default agent gives adopters an oriented first-run experience.

Change

1. Create claude-plugin/specorator/settings.json:

{
  "agent": "orchestrator"
}

2. Update scripts/build-claude-plugin.ts to include this file in the generated plugin package
3. Add presence check to check:claude-plugin.ts

Decision already made in #444

Recommended: Ship orchestrator as default agent in settings.json.

Definition of Done

• claude-plugin/specorator/settings.json exists with {"agent": "orchestrator"}
• build:claude-plugin copies the file into the generated package
• check:claude-plugin validates its presence
• Verify gate green

References

• Parent audit: research: Claude plugin developer best-practices audit — gaps, standards, refactor opportunities #444 §2, R5
• Official plugin settings docs: https://code.claude.com/docs/en/plugins-reference