feat: Add comprehensive NL-43/NL-53 Communication Guide and command references

- Introduced a new communication guide detailing protocol basics, transport modes, and a quick startup checklist.
- Added a detailed list of commands with their functions and usage for NL-43/NL-53 devices.
- Created a verified quick reference for command formats to prevent common mistakes.
- Implemented an improvements document outlining critical fixes, security enhancements, reliability upgrades, and code quality improvements for the SLMM project.
- Enhanced the frontend with a new button to retrieve all device settings, along with corresponding JavaScript functionality.
- Added a test script for the new settings retrieval API endpoint to demonstrate its usage and validate functionality.

test_settings_endpoint.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+"""
+Test script to demonstrate the GET /api/nl43/{unit_id}/settings endpoint.
+
+This endpoint retrieves all current device settings for verification purposes.
+"""
+
+import asyncio
+import sys
+
+
+async def test_settings_retrieval():
+    """Test the settings retrieval functionality."""
+    from app.services import NL43Client
+
+    # Example configuration - adjust these to match your actual device
+    host = "192.168.1.100"  # Replace with your NL43 device IP
+    port = 80
+    unit_id = "NL43-001"
+
+    print(f"Connecting to NL43 device at {host}:{port}...")
+    print(f"Unit ID: {unit_id}\n")
+
+    client = NL43Client(host, port)
+
+    try:
+        print("Retrieving all device settings...")
+        settings = await client.get_all_settings()
+
+        print("\n" + "="*60)
+        print("DEVICE SETTINGS SUMMARY")
+        print("="*60)
+
+        for key, value in settings.items():
+            print(f"{key:.<30} {value}")
+
+        print("="*60)
+        print(f"\nTotal settings retrieved: {len(settings)}")
+        print("\n✓ Settings retrieval successful!")
+
+    except ConnectionError as e:
+        print(f"\n✗ Connection Error: {e}")
+        print("\nTroubleshooting:")
+        print("  1. Verify the device IP address and port")
+        print("  2. Ensure the device is powered on and connected to the network")
+        print("  3. Check firewall settings")
+        sys.exit(1)
+
+    except Exception as e:
+        print(f"\n✗ Error: {e}")
+        sys.exit(1)
+
+
+async def test_api_endpoint():
+    """Demonstrate how to call the API endpoint."""
+    print("\n" + "="*60)
+    print("API ENDPOINT USAGE")
+    print("="*60)
+    print("\nTo retrieve all settings via the API, use:")
+    print("\n  GET /api/nl43/{unit_id}/settings")
+    print("\nExample with curl:")
+    print("\n  curl http://localhost:8000/api/nl43/NL43-001/settings")
+    print("\nExample response:")
+    print("""
+{
+  "status": "ok",
+  "unit_id": "NL43-001",
+  "settings": {
+    "measurement_state": "Stop",
+    "frequency_weighting": "A",
+    "time_weighting": "F",
+    "measurement_time": "00:01:00",
+    "leq_interval": "1s",
+    "lp_interval": "125ms",
+    "index_number": "0",
+    "battery_level": "100%",
+    "clock": "2025/12/24,20:45:30",
+    "sleep_mode": "Off",
+    "ftp_status": "On"
+  }
+}
+""")
+    print("="*60)
+
+
+if __name__ == "__main__":
+    print("NL43 Settings Retrieval Test")
+    print("="*60)
+    print("\nThis test demonstrates the new /api/nl43/{unit_id}/settings endpoint")
+    print("which allows you to view all current device settings for verification.\n")
+
+    # Show API usage
+    asyncio.run(test_api_endpoint())
+
+    # Uncomment below to test actual device connection
+    # asyncio.run(test_settings_retrieval())
+
+    print("\n✓ Test completed!")