feat(agent-development): add create-agent-skeleton.sh script (#30)

## Summary

Add a utility script to generate agent skeleton files with valid
structure, consistent with the existing `validate-agent.sh` and
`test-agent-trigger.sh` scripts.

## Problem

Fixes #26

The agent-development skill had scripts to validate and test agents, but
no script to create them. Users had to manually create agent files from
scratch, which was error-prone and inconsistent.

## Solution

Created `create-agent-skeleton.sh` that:
- Validates agent names (lowercase, alphanumeric + hyphens, 3-50 chars)
- Generates properly formatted YAML frontmatter
- Includes placeholder examples and system prompt sections
- Provides color-coded output consistent with other scripts
- Guides users through next steps after creation

### Alternatives Considered

1. **Template file only** - Rejected because it doesn't validate names
or prevent overwriting existing files
2. **Interactive wizard** - Rejected as over-engineered for the use
case; current approach is simpler and follows existing script patterns

## Changes

-
`plugins/plugin-dev/skills/agent-development/scripts/create-agent-skeleton.sh`:
New 170-line script
- `plugins/plugin-dev/skills/agent-development/SKILL.md`: Added script
reference and updated workflow

## Testing

- [x] Tests added/updated (manual testing)
- [x] All tests passing
- [x] Linting passes (shellcheck, markdownlint)

### Manual Test Results

```bash
# Help message
./create-agent-skeleton.sh
# ✅ Shows usage information

# Invalid name rejection
./create-agent-skeleton.sh Invalid-Name /tmp
# ✅ Rejects uppercase, shows helpful error

# Valid agent creation
./create-agent-skeleton.sh test-agent /tmp
# ✅ Creates skeleton file with valid structure

# Validation passes
./validate-agent.sh /tmp/test-agent.md
# ✅ Generated file passes validation

# Duplicate rejection
./create-agent-skeleton.sh test-agent /tmp
# ✅ Rejects when file exists
```

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

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

Author: sjnims

plugins/plugin-dev/skills/agent-development/SKILL.md

@@ -477,6 +477,7 @@ Working examples in `examples/`:
 
 Development tools in `scripts/`:
 
+- **`create-agent-skeleton.sh`** - Generate new agent file from template
 - **`validate-agent.sh`** - Validate agent file structure
 - **`test-agent-trigger.sh`** - Test if agent triggers correctly
 
@@ -486,7 +487,7 @@ To create an agent for a plugin:
 
 1. Define agent purpose and triggering conditions
 2. Choose creation method (AI-assisted or manual)
-3. Create `agents/agent-name.md` file
+3. Create agent file using skeleton: `./skills/agent-development/scripts/create-agent-skeleton.sh agent-name agents/`
 4. Write frontmatter with all required fields
 5. Write system prompt following best practices
 6. Include 2-4 triggering examples in description

plugins/plugin-dev/skills/agent-development/scripts/create-agent-skeleton.sh

@@ -0,0 +1,176 @@
+#!/bin/bash
+# Agent Skeleton Generator
+# Creates a new agent file with correct structure
+
+set -euo pipefail
+
+# Usage
+if [ $# -eq 0 ]; then
+  echo "Usage: $0 <agent-name> [output-dir]"
+  echo ""
+  echo "Creates a skeleton agent file with:"
+  echo "  - Valid YAML frontmatter"
+  echo "  - Placeholder description with example block"
+  echo "  - Basic system prompt structure"
+  echo ""
+  echo "Arguments:"
+  echo "  agent-name   Agent identifier (lowercase, numbers, hyphens)"
+  echo "  output-dir   Directory to create file in (default: current directory)"
+  echo ""
+  echo "Examples:"
+  echo "  $0 code-reviewer agents/"
+  echo "  $0 test-generator"
+  echo ""
+  echo "After creation:"
+  echo "  1. Edit the file to fill in placeholders"
+  echo "  2. Add 2-4 triggering examples"
+  echo "  3. Write detailed system prompt"
+  echo "  4. Validate: ./scripts/validate-agent.sh <output-file>"
+  echo "  5. Test triggers: ./scripts/test-agent-trigger.sh <output-file>"
+  exit 1
+fi
+
+AGENT_NAME="$1"
+OUTPUT_DIR="${2:-.}"
+OUTPUT_FILE="$OUTPUT_DIR/$AGENT_NAME.md"
+
+echo "🔍 Creating agent skeleton: $AGENT_NAME"
+echo ""
+
+# Validate name format (lowercase alphanumeric + hyphens, 3-50 chars)
+if ! [[ "$AGENT_NAME" =~ ^[a-z0-9][a-z0-9-]*[a-z0-9]$ ]]; then
+  echo "❌ Invalid name: $AGENT_NAME"
+  echo ""
+  echo "Agent names must:"
+  echo "  - Start with a lowercase letter or number"
+  echo "  - End with a lowercase letter or number"
+  echo "  - Contain only lowercase letters, numbers, and hyphens"
+  echo "  - Be at least 3 characters long"
+  echo ""
+  echo "Valid examples: code-reviewer, test-gen, my-agent-123"
+  echo "Invalid examples: Code-Reviewer, -agent, agent-, a"
+  exit 1
+fi
+echo "✅ Name format valid"
+
+# Validate name length
+name_length=${#AGENT_NAME}
+if [ "$name_length" -lt 3 ]; then
+  echo "❌ Name too short: $name_length characters (minimum 3)"
+  exit 1
+fi
+if [ "$name_length" -gt 50 ]; then
+  echo "❌ Name too long: $name_length characters (maximum 50)"
+  exit 1
+fi
+echo "✅ Name length valid ($name_length characters)"
+
+# Check output directory exists
+if [ ! -d "$OUTPUT_DIR" ]; then
+  echo "❌ Directory does not exist: $OUTPUT_DIR"
+  echo ""
+  echo "Create it first with: mkdir -p $OUTPUT_DIR"
+  exit 1
+fi
+echo "✅ Output directory exists"
+
+# Check file doesn't already exist
+if [ -f "$OUTPUT_FILE" ]; then
+  echo "❌ File already exists: $OUTPUT_FILE"
+  echo ""
+  echo "Options:"
+  echo "  - Choose a different name"
+  echo "  - Delete the existing file: rm $OUTPUT_FILE"
+  echo "  - Edit the existing file directly"
+  exit 1
+fi
+echo "✅ Output path available"
+
+echo ""
+echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
+echo "📝 Creating agent file..."
+echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
+echo ""
+
+# Create the agent skeleton file
+cat > "$OUTPUT_FILE" << EOF
+---
+name: $AGENT_NAME
+description: Use this agent when [describe triggering conditions]. Examples:
+
+<example>
+Context: [Describe the situation]
+user: "[What the user says]"
+assistant: "[How Claude responds before triggering]"
+<commentary>
+[Why this agent should trigger]
+</commentary>
+assistant: "I'll use the $AGENT_NAME agent to [action]."
+</example>
+
+<example>
+Context: [Second example situation]
+user: "[Another user request]"
+assistant: "[Claude's response]"
+<commentary>
+[Explanation of why this triggers the agent]
+</commentary>
+</example>
+
+model: inherit
+color: blue
+---
+
+You are [describe the agent's role and expertise].
+
+**Your Core Responsibilities:**
+
+1. [Primary responsibility]
+2. [Secondary responsibility]
+3. [Additional responsibility]
+
+**Process:**
+
+1. [First step]
+2. [Second step]
+3. [Third step]
+
+**Quality Standards:**
+
+- [Standard 1]
+- [Standard 2]
+- [Standard 3]
+
+**Output Format:**
+
+Provide results as:
+
+- [What to include]
+- [How to structure]
+EOF
+
+echo "✅ Created agent skeleton: $OUTPUT_FILE"
+echo ""
+echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
+echo "📋 Next Steps"
+echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
+echo ""
+echo "1. Edit the file to fill in placeholders:"
+echo "   - Replace [bracketed text] with actual content"
+echo "   - Update description to explain when agent triggers"
+echo "   - Write 2-4 triggering examples"
+echo "   - Develop detailed system prompt"
+echo ""
+echo "2. Choose appropriate settings:"
+echo "   - model: inherit (default), sonnet, opus, or haiku"
+echo "   - color: blue (default), cyan, green, yellow, magenta, or red"
+echo "   - tools: Add array if restricting tools (optional)"
+echo ""
+echo "3. Validate the agent:"
+echo "   ./scripts/validate-agent.sh $OUTPUT_FILE"
+echo ""
+echo "4. Test triggering:"
+echo "   ./scripts/test-agent-trigger.sh $OUTPUT_FILE"
+echo ""
+echo "5. Load in Claude Code:"
+echo "   cc --plugin-dir /path/to/plugin"