docs: fix second-person writing style in marketplace-structure skill

Change "you have access" to "access is available" in distribution-patterns.md
to maintain imperative/infinitive form per skill-development best practices.

Fixes #94

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: sjnims

plugins/plugin-dev/skills/marketplace-structure/references/distribution-patterns.md

@@ -296,7 +296,7 @@ Before adding external plugins to your marketplace:
 
 1. Verify plugin source URL is accessible
 2. Check plugin directory contains required files
-3. For GitHub sources, ensure repository is public or you have access
+3. For GitHub sources, ensure repository is public or access is available
 4. Test plugin sources manually by cloning
 
 ### Validation Commands