Fix YAML frontmatter parsing errors in agent description fields

Use YAML block scalars (|) for multi-line description fields that contain
<example> blocks with colons and special characters. Without block scalars,
the YAML parser fails because it interprets lines like 'user:' and
'assistant:' as new key-value pairs.

Affected files:
- plugins/plugin-dev/agents/agent-creator.md
- plugins/plugin-dev/agents/skill-reviewer.md
- plugins/plugin-dev/agents/plugin-validator.md
- plugins/pr-review-toolkit/agents/code-simplifier.md

plugins/plugin-dev/agents/agent-creator.md

@@ -1,6 +1,7 @@
 ---
 name: agent-creator
-description: Use this agent when the user asks to "create an agent", "generate an agent", "build a new agent", "make me an agent that...", or describes agent functionality they need. Trigger when user wants to create autonomous agents for plugins. Examples:
+description: |
+  Use this agent when the user asks to "create an agent", "generate an agent", "build a new agent", "make me an agent that...", or describes agent functionality they need. Trigger when user wants to create autonomous agents for plugins. Examples:
 
   <example>
   Context: User wants to create a code review agent
@@ -28,7 +29,6 @@ assistant: "I'll use the agent-creator agent to generate a configuration validat
   Plugin development with agent addition, trigger agent-creator.
   </commentary>
   </example>
-
 model: sonnet
 color: magenta
 tools: ["Write", "Read"]

plugins/plugin-dev/agents/plugin-validator.md

@@ -1,6 +1,7 @@
 ---
 name: plugin-validator
-description: Use this agent when the user asks to "validate my plugin", "check plugin structure", "verify plugin is correct", "validate plugin.json", "check plugin files", or mentions plugin validation. Also trigger proactively after user creates or modifies plugin components. Examples:
+description: |
+  Use this agent when the user asks to "validate my plugin", "check plugin structure", "verify plugin is correct", "validate plugin.json", "check plugin files", or mentions plugin validation. Also trigger proactively after user creates or modifies plugin components. Examples:
 
   <example>
   Context: User finished creating a new plugin
@@ -30,7 +31,6 @@ Manifest modified, validate to ensure correctness.
   </commentary>
   assistant: "I'll use the plugin-validator agent to check the manifest."
   </example>
-
 model: inherit
 color: yellow
 tools: ["Read", "Grep", "Glob", "Bash"]

plugins/plugin-dev/agents/skill-reviewer.md

@@ -1,6 +1,7 @@
 ---
 name: skill-reviewer
-description: Use this agent when the user has created or modified a skill and needs quality review, asks to "review my skill", "check skill quality", "improve skill description", or wants to ensure skill follows best practices. Trigger proactively after skill creation. Examples:
+description: |
+  Use this agent when the user has created or modified a skill and needs quality review, asks to "review my skill", "check skill quality", "improve skill description", or wants to ensure skill follows best practices. Trigger proactively after skill creation. Examples:
 
   <example>
   Context: User just created a new skill
@@ -29,7 +30,6 @@ assistant: "I'll use the skill-reviewer agent to review the changes."
   Skill description modified, review for triggering effectiveness.
   </commentary>
   </example>
-
 model: inherit
 color: cyan
 tools: ["Read", "Grep", "Glob"]

plugins/pr-review-toolkit/agents/code-simplifier.md

@@ -1,6 +1,11 @@
 ---
 name: code-simplifier
-description: Use this agent when code has been written or modified and needs to be simplified for clarity, consistency, and maintainability while preserving all functionality. This agent should be triggered automatically after completing a coding task or writing a logical chunk of code. It simplifies code by following project best practices while retaining all functionality. The agent focuses only on recently modified code unless instructed otherwise.\n\nExamples:\n\n<example>
+description: |
+  Use this agent when code has been written or modified and needs to be simplified for clarity, consistency, and maintainability while preserving all functionality. This agent should be triggered automatically after completing a coding task or writing a logical chunk of code. It simplifies code by following project best practices while retaining all functionality. The agent focuses only on recently modified code unless instructed otherwise.
+
+  Examples:
+
+  <example>
   Context: The assistant has just implemented a new feature that adds user authentication to an API endpoint.
   user: "Please add authentication to the /api/users endpoint"
   assistant: "I've implemented the authentication for the /api/users endpoint. Here's the code:"