docs(contributing): no documented way to test framework changes locally #245

Problem

CONTRIBUTING.md documents setup, commits (DCO), and the PR flow, but never tells a contributor how to load their working tree into a real project and exercise the skills they changed before opening a PR. The only adjacent hint lives in docs/CREATE_PLUGIN.md (Step 4), and it targets creating a new plugin, not iterating on the existing ones - and it never mentions the directory marketplace / .claude/settings.local.json pattern that lets you pin a personal project to a local checkout.

Expected

A "Test your changes locally" section in CONTRIBUTING.md covering:

• the Claude Code path (/plugin marketplace add + /plugin install + /reload-plugins);
• pinning a personal project to the local checkout via a directory marketplace in settings.local.json.