docs: fix second-person usage in mcp-integration skill (#81)

## Summary

Fix second-person pronoun usage ("you're") in the mcp-integration skill
reference file to follow skill writing style guidelines requiring
imperative form.

## Problem

Fixes #79

The skill reference file used second-person ("Ensure you're
authenticated") in instructional text at line 409, violating the skill
development guidelines which require imperative/infinitive form.

## Solution

Changed "Ensure you're authenticated to Asana before running this
command." to "Ensure authentication to Asana before running this
command." using Option 1 from the issue.

### Alternatives Considered

- **Option 2 (passive)**: "Authentication to Asana is required before
running this command." - More natural but less consistent with
imperative style used elsewhere.

## Changes

- `plugins/plugin-dev/skills/mcp-integration/references/tool-usage.md`:
Line 409 updated to imperative form

## Testing

- [x] Markdownlint passes
- [x] Change follows skill writing style guidelines

---
🤖 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