Clarify that Skill tool loads skill content directly

Fixes pattern where Claude would invoke a skill then try to Read the
file separately. The Skill tool already provides the content.

- Add "How to Access Skills" section to using-superpowers
- Change "read the skill" → "invoke the skill"
- Commands now use fully qualified names (superpowers:brainstorming etc)

skills/using-superpowers/SKILL.md

@@ -4,13 +4,19 @@ description: Use when starting any conversation - establishes how to find and us
 ---
 
 <EXTREMELY-IMPORTANT>
-If you think there is even a 1% chance a skill might apply to what you are doing, you ABSOLUTELY MUST read the skill.
+If you think there is even a 1% chance a skill might apply to what you are doing, you ABSOLUTELY MUST invoke the skill.
 
 IF A SKILL APPLIES TO YOUR TASK, YOU DO NOT HAVE A CHOICE. YOU MUST USE IT.
 
 This is not negotiable. This is not optional. You cannot rationalize your way out of this.
 </EXTREMELY-IMPORTANT>
 
+## How to Access Skills
+
+**In Claude Code:** Use the `Skill` tool. When you invoke a skill, its content is loaded and presented to you—follow it directly. Never use the Read tool on skill files.
+
+**In other environments:** Check your platform's documentation for how skills are loaded.
+
 # Using Skills
 
 ## The Rule