feat(skills): modernize capability-writing with Anthropic best practices

Updates capability-writing skill with progressive disclosure structure based on
Anthropic's January 2025 documentation. Implements Haiku-first approach (12x
cheaper, 2-5x faster than Sonnet).

Key changes:
- Add 5 core principles: conciseness, progressive disclosure, script bundling,
  degrees of freedom, and Haiku-first model selection
- Restructure with best-practices.md, templates/, examples/, and reference/
- Create 4 templates: user-invocable skill, background skill, agent, helper script
- Add 3 examples: simple workflow, progressive disclosure, with scripts
- Add 3 reference docs: frontmatter fields, model selection, anti-patterns
- Update create-capability to analyze complexity and recommend structures
- Default all new skills/agents to Haiku unless justified

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

skills/capability-writing/templates/helper-script.sh

@@ -0,0 +1,86 @@
+#!/bin/bash
+# script-name.sh - Brief description of what this script does
+#
+# Usage: script-name.sh <param1> <param2> [optional-param]
+#
+# Example:
+#   script-name.sh value1 value2
+#   script-name.sh value1 value2 optional-value
+#
+# Exit codes:
+#   0 - Success
+#   1 - Invalid arguments or general error
+#   2 - Specific error condition (document what)
+
+set -e  # Exit immediately on error
+# set -x  # Uncomment for debugging
+
+# Color output for better visibility
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m' # No Color
+
+# Helper functions
+error() {
+    echo -e "${RED}ERROR: $1${NC}" >&2
+    exit 1
+}
+
+success() {
+    echo -e "${GREEN}SUCCESS: $1${NC}"
+}
+
+warn() {
+    echo -e "${YELLOW}WARNING: $1${NC}"
+}
+
+# Input validation
+if [ $# -lt 2 ]; then
+    echo "Usage: $0 <param1> <param2> [optional-param]"
+    echo ""
+    echo "Description: Brief description of what this does"
+    echo ""
+    echo "Arguments:"
+    echo "  param1        Description of param1"
+    echo "  param2        Description of param2"
+    echo "  optional-param  Description of optional param (default: value)"
+    exit 1
+fi
+
+# Parse arguments
+PARAM1=$1
+PARAM2=$2
+OPTIONAL_PARAM=${3:-"default-value"}
+
+# Validate inputs
+if [ -z "$PARAM1" ]; then
+    error "param1 cannot be empty"
+fi
+
+# Main logic
+main() {
+    echo "Processing with param1=$PARAM1, param2=$PARAM2..."
+
+    # Step 1: Describe what this step does
+    if ! some_command "$PARAM1"; then
+        error "Failed to process param1"
+    fi
+
+    # Step 2: Another operation with error handling
+    result=$(another_command "$PARAM2" 2>&1)
+    if [ $? -ne 0 ]; then
+        error "Failed to process param2: $result"
+    fi
+
+    # Step 3: Validation
+    if [ ! -f "$result" ]; then
+        error "Expected file not found: $result"
+    fi
+
+    success "Operation completed successfully"
+    echo "$result"  # Output for caller to parse
+}
+
+# Execute main function
+main