docs: fix second-person usage in mcp-integration skill

Change "Ensure you're authenticated" to imperative form
"Ensure authentication" to follow skill writing style guidelines.

Fixes #79

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

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

Author: sjnims

plugins/plugin-dev/skills/mcp-integration/references/tool-usage.md

@@ -406,7 +406,7 @@ This command uses the following Asana MCP tools:
 - **asana_create_task**: Create new task with details
 - **asana_update_task**: Update existing task properties
 
-Ensure you're authenticated to Asana before running this command.
+Ensure authentication to Asana before running this command.
 ```
 
 ## Testing Tool Usage