Adds LNbits Borg backup module

Implements a new module for backing up LNbits data using Borg.

This module automates hourly backups, encrypts the data, and provides point-in-time recovery. It includes scripts for listing, restoring, and mounting backups. A comprehensive setup guide is provided in the documentation.

The configuration allows specifying the Borg repository location, schedule, compression settings, retention policy, and SSH key for secure access.

config/machines/example-machine/borg-lnbits.nix

@@ -0,0 +1,35 @@
+{ config, pkgs, ... }:
+
+{
+  imports = [
+    ./modules/lnbits-backup.nix  # Add this line
+  ];
+
+  # Enable LNbits Borg backup
+  services.lnbits-backup = {
+    enable = true;
+
+    # Repository path - update with your actual path
+    # Option 1: Traditional format
+    # repository = "borg@192.168.1.100:/mnt/my_ssd/borg-backups/lnbits";
+
+    # Option 2: Full SSH URL format (note double slash for absolute path)
+    repository = "ssh://borg@<your-backup-ip>//mnt/borg-backups/lnbits";
+
+    # Backup schedule
+    schedule = "*:0/15";  # Backup schedule (hourly, daily, or systemd timer format)
+
+    # Compression with auto-detection
+    # "auto" skips compression for already-compressed files (images, videos, etc.)
+    compression = "auto,lz4";      # For Raspberry Pi (faster)
+    # compression = "auto,zstd";   # For RockPro64 (better compression)
+
+    # Retention policy, leave all of these
+    retention = {
+      hourly = 24;   # Last 24 hours
+      daily = 7;     # Last 7 days
+      weekly = 4;    # Last 4 weeks
+      monthly = 6;   # Last 6 months
+    };
+  };
+}