fix(pr-review-toolkit): make code-reviewer frontmatter valid YAML

[Rohan5commit]

Summary

• rewrite the code-reviewer frontmatter description as a YAML block scalar
• preserve the embedded trigger examples while making the agent file parse cleanly

Related Issue

• Part of Official plugins have YAML/XML syntax errors (agnix lint) #40370

Guideline Alignment

• one focused syntax fix in a single maintained plugin file
• no behavioral or unrelated review workflow changes

Validation

• ruby -e 'require "yaml"; ...' to confirm the frontmatter parses and keeps the examples
• git diff --check

[Copilot]

Pull request overview

This PR fixes YAML frontmatter parsing for the code-reviewer agent by converting the description field into a valid YAML block scalar while preserving the embedded example markup.

Changes:

• Replaced the single-line description: string (with escaped newlines and embedded tags) with a YAML block scalar (description: |).
• Preserved the existing <example> / <commentary> / <function ...> content in a YAML-safe format.

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