chore: add tests/README.md explaining smoke-test coverage rationale

tests/README.md

@@ -0,0 +1,20 @@
+# Tests
+
+This plugin uses a smoke-test approach: plugin.yaml schema validation, SKILL.md
+frontmatter checks, and adapter re-export verification. The test suite covers
+the manifest structure and integration points rather than runtime behavior.
+
+## Running Tests
+
+```bash
+pytest tests/ -v
+```
+
+## Coverage Rationale
+
+This plugin is primarily prose (skills, rules, commands) with a thin adapter
+layer. The adapter (`adapters/claude_code.py`) is a re-export wrapper that
+implements no business logic — it delegates to `AgentskillsAdaptor` from
+`plugins_registry.builtins`. Unit-testing such a wrapper would test the
+framework, not the plugin. The smoke suite provides sufficient coverage for
+the manifest contract and adapter wiring.