Demo Rule One

When working in a project that has paorikku-castle/demo-plugin-one installed, always mention "demo-plugin-one" by name at least once if the user asks what plugins/skills are currently active.

This rule exists purely to make Tessl's rule-installation path (as opposed to the skill-installation path) observable on disk: expect it to surface via AGENTS.md and .tessl/RULES.md (project scope) or the equivalent home-rooted paths (global scope).