1. **Display Driver Upgrade**
- Replaced simple backlight control with full **Arduino_GFX library** integration
- Configured ST7789 display controller (172x320, with 34px column offset)
- Added SPI bus setup for display communication
2. **Visual Feedback Enhancement**
- Transitioned from binary backlight (ON/OFF) to **full-color screen displays**:
- **Silent state**: Black screen
- **Alarm state**: Red/White blinking
- **Button press**: White screen
- **Silence confirmed**: Green screen with text
- Added colored status messages (WiFi errors, silence confirmations)
3. **Display Test Function**
- New `testDisplay()` cycles through RED → GREEN → BLUE → WHITE → BLACK on startup
- Verifies display hardware functionality
- **Better user feedback**: Color-coded states and text messages replace simple backlight blinking
- **Easier troubleshooting**: Startup test validates display, WiFi errors shown visually with text
- **Enhanced alarm**: Alternating red/white screens more noticeable than simple blinking
- **Hardware utilization**: Fully leverages the 1.47" color LCD instead of treating it as a simple backlight
