Fix manifest icon references and add file reference linter

Manifest fixes:
- Updated all icon references from .png to .svg files
- Changed MIME types from image/png to image/svg+xml
- Removed missing screenshots section
- Fixed HTML favicon references to use SVG files

New reference linter (lint-references.py):
- Validates all file references in HTML and manifest files
- Checks that referenced files actually exist
- Prevents broken links and missing assets
- Integrated into justfile as 'validate-references'
- Added to check-all command for comprehensive validation

Justfile enhancements:
- Added validate-references command
- Updated check-all to include reference validation
- Enhanced validate command with reference checking

Documentation updates:
- Updated CLAUDE.md with reference validation info
- Added file reference checking to code quality standards

This prevents issues where manifest/HTML reference non-existent files,
improving PWA reliability and catching asset mismatches early.

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

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

lint-references.py

@@ -0,0 +1,147 @@
+#!/usr/bin/env python3
+"""
+Reference validator for GlitchCraft
+Checks that all file references in HTML and manifest actually exist
+"""
+
+import json
+import os
+import re
+import sys
+from pathlib import Path
+
+
+def check_file_exists(file_path, base_dir):
+    """Check if a file exists relative to base directory."""
+    full_path = base_dir / file_path
+    return full_path.exists()
+
+
+def extract_html_references(html_content):
+    """Extract file references from HTML content."""
+    references = []
+    
+    # Link href attributes
+    for match in re.finditer(r'<link[^>]+href=["\']([^"\']+)["\']', html_content):
+        href = match.group(1)
+        if not href.startswith(('http://', 'https://', '//', 'data:', '#')):
+            references.append(href)
+    
+    # Script src attributes
+    for match in re.finditer(r'<script[^>]+src=["\']([^"\']+)["\']', html_content):
+        src = match.group(1)
+        if not src.startswith(('http://', 'https://', '//', 'data:')):
+            references.append(src)
+    
+    # Image src attributes
+    for match in re.finditer(r'<img[^>]+src=["\']([^"\']+)["\']', html_content):
+        src = match.group(1)
+        if not src.startswith(('http://', 'https://', '//', 'data:')):
+            references.append(src)
+    
+    return references
+
+
+def extract_manifest_references(manifest_data):
+    """Extract file references from manifest JSON."""
+    references = []
+    
+    # Icon sources
+    if 'icons' in manifest_data:
+        for icon in manifest_data['icons']:
+            if 'src' in icon:
+                references.append(icon['src'])
+    
+    # Screenshot sources
+    if 'screenshots' in manifest_data:
+        for screenshot in manifest_data['screenshots']:
+            if 'src' in screenshot:
+                references.append(screenshot['src'])
+    
+    return references
+
+
+def check_html_file(file_path, base_dir):
+    """Check all references in an HTML file."""
+    errors = []
+    
+    try:
+        with open(file_path, 'r', encoding='utf-8') as f:
+            content = f.read()
+        
+        references = extract_html_references(content)
+        
+        for ref in references:
+            if not check_file_exists(ref, base_dir):
+                errors.append(f"Missing file: {ref}")
+                
+    except Exception as e:
+        errors.append(f"Error reading {file_path}: {e}")
+    
+    return errors
+
+
+def check_manifest_file(file_path, base_dir):
+    """Check all references in a manifest file."""
+    errors = []
+    
+    try:
+        with open(file_path, 'r', encoding='utf-8') as f:
+            manifest_data = json.load(f)
+        
+        references = extract_manifest_references(manifest_data)
+        
+        for ref in references:
+            if not check_file_exists(ref, base_dir):
+                errors.append(f"Missing file: {ref}")
+                
+    except Exception as e:
+        errors.append(f"Error reading {file_path}: {e}")
+    
+    return errors
+
+
+def main():
+    """Main function to check all references."""
+    script_dir = Path(__file__).parent
+    app_dir = script_dir / 'app'
+    
+    print("🔍 Checking file references...")
+    
+    total_errors = 0
+    
+    # Check HTML files
+    html_files = list(app_dir.glob('*.html'))
+    for html_file in html_files:
+        errors = check_html_file(html_file, app_dir)
+        if errors:
+            print(f"\n❌ {html_file.name}:")
+            for error in errors:
+                print(f"  • {error}")
+                total_errors += 1
+        else:
+            print(f"✅ {html_file.name}")
+    
+    # Check manifest file
+    manifest_file = app_dir / 'manifest.json'
+    if manifest_file.exists():
+        errors = check_manifest_file(manifest_file, app_dir)
+        if errors:
+            print(f"\n❌ manifest.json:")
+            for error in errors:
+                print(f"  • {error}")
+                total_errors += 1
+        else:
+            print("✅ manifest.json")
+    
+    # Summary
+    if total_errors == 0:
+        print(f"\n🎉 All file references are valid!")
+        return 0
+    else:
+        print(f"\n💥 Found {total_errors} reference error(s)")
+        return 1
+
+
+if __name__ == '__main__':
+    sys.exit(main())