style: suppress grep stderr in test-agent-trigger.sh (#150)

## Description

Add `2>/dev/null` to suppress potential stderr output from grep when
counting example blocks in `test-agent-trigger.sh`.

```bash
# Before
EXAMPLE_COUNT=$(echo "$DESCRIPTION" | grep -c '<example>' || echo 0)

# After
EXAMPLE_COUNT=$(echo "$DESCRIPTION" | grep -c '<example>' 2>/dev/null || echo 0)
```

The `|| echo 0` already handles grep's non-zero exit code when no
matches are found. This change additionally suppresses any error
messages grep might emit to stderr in edge cases.

## Type of Change

- [ ] Bug fix (non-breaking change that fixes an issue)
- [ ] New feature (non-breaking change that adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] Documentation update (improvements to README, CLAUDE.md, or
component docs)
- [x] Refactoring (code change that neither fixes a bug nor adds a
feature)
- [ ] Configuration change (changes to .markdownlint.json, plugin.json,
etc.)

## Component(s) Affected

- [ ] Commands (`/plugin-dev:*`)
- [x] Skills (methodology and best practices)
- [ ] Agents (requirements-assistant)
- [ ] Hooks (UserPromptSubmit)
- [ ] Documentation (README.md, CLAUDE.md, SECURITY.md)
- [ ] Configuration (.markdownlint.json, plugin.json, marketplace.json)
- [ ] Issue/PR templates
- [ ] Other (please specify):

## Motivation and Context

Minor robustness improvement identified during code review. While
unlikely to cause issues in practice, suppressing stderr is a defensive
coding practice that prevents unexpected error messages from appearing
in output.

## How Has This Been Tested?

**Test Configuration**:
- Claude Code version: Latest
- GitHub CLI version: 2.x
- OS: macOS
- Testing repository: N/A

**Test Steps**:
1. Run `test-agent-trigger.sh` with a valid agent file
2. Verify example count is correctly reported
3. Verify no stderr output appears

## Checklist

### General

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas
(if applicable)
- [x] My changes generate no new warnings or errors

### Documentation

- [ ] I have updated the documentation accordingly (README.md,
CLAUDE.md, or component docs)
- [ ] I have updated YAML frontmatter (if applicable)
- [ ] I have verified all links work correctly

### Markdown

- [x] I have run `markdownlint` and fixed all issues
- [x] My markdown follows the repository style (ATX headers, dash lists,
fenced code blocks)
- [ ] I have verified special HTML elements are properly closed
(`<example>`, `<commentary>`, etc.)

### Component-Specific Checks

N/A - This is a shell script utility, not a command/skill/agent.

### Testing

- [ ] I have tested the plugin locally with `cc --plugin-dir
plugins/plugin-dev`
- [ ] I have tested the full workflow (if applicable)
- [ ] I have verified GitHub CLI integration works (if applicable)
- [ ] I have tested in a clean repository (not my development repo)

### Version Management (if applicable)

- [ ] I have updated version numbers in both `plugin.json` and
`marketplace.json` (if this is a release)
- [ ] I have updated CHANGELOG.md with relevant changes

## Screenshots (if applicable)

N/A

## Additional Notes

This is a minor robustness improvement. The original code was
functional; this change is purely defensive.

## Reviewer Notes

**Areas that need special attention**:
- None - this is a trivial change

**Known limitations or trade-offs**:
- None

---

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

Co-authored-by: Claude <noreply@anthropic.com>

Author: sjnims

plugins/plugin-dev/skills/agent-development/scripts/test-agent-trigger.sh

@@ -70,7 +70,7 @@ if [ -z "$DESCRIPTION" ]; then
 fi
 
 # Count example blocks
-EXAMPLE_COUNT=$(echo "$DESCRIPTION" | grep -c '<example>' || echo 0)
+EXAMPLE_COUNT=$(echo "$DESCRIPTION" | grep -c '<example>' 2>/dev/null || echo 0)
 
 echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
 echo "📊 EXAMPLE ANALYSIS"