Plan: Add Progressive Web App (PWA) Support to Emoncms

• Create web app manifest file (manifest.json) with app metadata, icons, and display settings
• Create PWA icon files in multiple sizes (192x192, 512x512) for proper mobile display
• Create service worker (service-worker.js) for offline capabilities and caching
• Update Theme/theme.php to include manifest link and theme-color meta tags in HTML head
• Register service worker in the main JavaScript initialization
• Address code review feedback (path validation, CORS support, better offline handling)
• Fix manifest icon purpose format and improve caching for opaque responses
• Pass CodeQL security checks
• Update icons with OpenEnergyMonitor logo per maintainer request
• Complete implementation

Summary of Implementation

Files Created:

1. manifest.json - Web app manifest with metadata and icon references
2. service-worker.js - Service worker for offline caching and functionality
3. Theme/pwa-icon-192.png - 192x192 app icon with OpenEnergyMonitor logo
4. Theme/pwa-icon-512.png - 512x512 app icon with OpenEnergyMonitor logo

Files Modified:

1. Theme/theme.php - Added manifest link, theme-color, and apple-mobile-web-app-capable meta tags
2. Lib/emoncms.js - Added service worker registration with proper validation

PWA Features:

• ✅ Installable on mobile and desktop devices
• ✅ Standalone display mode
• ✅ Offline functionality with intelligent caching
• ✅ CORS and opaque response support
• ✅ Smart offline fallback for navigation and resources
• ✅ Theme color integration (#44b3e2)
• ✅ OpenEnergyMonitor branded icons
• ✅ Multiple icon purposes (any and maskable)

Security:

• ✅ No vulnerabilities detected by CodeQL
• ✅ Proper error handling in service worker
• ✅ Safe caching strategy

• Fixes Add progressive web app (PWA) support #1959

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