Implement Electronic Shelf Label (ESL) BLE Service

[Copilot]

This PR implements a complete Electronic Shelf Label (ESL) Bluetooth Low Energy service for the PSLabel smart eInk labeling system, following the Bluetooth ESL specification.

Features Implemented

ESL Service Architecture

• ESL Service (UUID: 0x181D) with four main characteristics:
  • Control Point (0x2BE1): Commands for display control (update, clear, sleep, wake, status)
  • Image Transfer (0x2BE2): Wireless transfer of display image data with 1KB buffering
  • Display Information (0x2BE3): Device capability reporting (resolution, color depth, display type)
  • Status (0x2BE4): Real-time device status with notification support

Key Capabilities

• BLE GATT service following standard ESL specification
• Command processing for display lifecycle management
• Image data transfer with size prefixing protocol
• Status notifications for real-time device monitoring
• Connection management with proper BLE callbacks
• Memory-efficient implementation suitable for embedded systems

Integration

• Complete main application integration with BLE advertising
• Added all necessary Bluetooth configuration to prj.conf
• Updated build system to include new ESL service files
• Comprehensive documentation and usage examples

Example Usage

// Connect to PSLabel device via BLE
// Read display capabilities
struct esl_display_info info;
// Transfer image data to device
// Send update command to refresh display

The service enables wireless communication with electronic shelf labels for retail, warehouse, and smart office applications, providing the foundation for the PSLabel ecosystem's smart labeling functionality.

Fixes #34.

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[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud