Refactor Nix package definition and enhance README for lidarr-mb-gap

- Updated `flake.nix` to import the new Nix package definition from `nix/package.nix`, streamlining the build process for the lidarr-mb-gap application.
- Enhanced the README.md to include new features such as NixOS module support for automated deployment, detailed deployment instructions, and configuration options for SSH and output directories.
- Added sections for troubleshooting output file issues and clarified the structure of the project, including new files for deployment and web serving.

nixos/lidarr-mb-gap.nix

@@ -3,6 +3,17 @@
 let
   reportDir = "/var/lib/lidarr-mb-gap/reports";
   envFile = "/var/lib/lidarr-mb-gap/.env";
+  
+  # Determine which package to use
+  lidarrMbGapPackage = if config.services.lidarr-mb-gap.package != null
+    then config.services.lidarr-mb-gap.package
+    else if config.services.lidarr-mb-gap.src != null
+      then import ../nix/package.nix {
+        inherit pkgs;
+        lib = pkgs.lib;
+        src = config.services.lidarr-mb-gap.src;
+      }
+      else throw "services.lidarr-mb-gap: Either 'package' or 'src' must be set.";
 in
 {
   options.services.lidarr-mb-gap = {
@@ -55,11 +66,35 @@ in
       default = "/var/www/html";
       description = "Path on VPS where reports should be synced";
     };
+    
+    sshKeyFile = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      description = "Path to SSH private key file for rsync. If null, uses default SSH key location.";
+    };
+    
+    sshKnownHosts = lib.mkOption {
+      type = lib.types.attrsOf (lib.types.submodule {
+        options = {
+          hostNames = lib.mkOption {
+            type = lib.types.listOf lib.types.str;
+            description = "List of hostnames/IPs for this known host";
+          };
+          publicKey = lib.mkOption {
+            type = lib.types.str;
+            description = "SSH public key for the host";
+          };
+        };
+      });
+      default = {};
+      description = "SSH known hosts configuration for the VPS (same format as programs.ssh.knownHosts)";
+    };
   };
 
   config = lib.mkIf config.services.lidarr-mb-gap.enable {
     systemd.tmpfiles.rules = [
       "d ${config.services.lidarr-mb-gap.reportDir} 0755 lidarr-mb-gap lidarr-mb-gap -"
+      "d /var/lib/lidarr-mb-gap/.ssh 0700 lidarr-mb-gap lidarr-mb-gap -"
     ];
 
     users.users.lidarr-mb-gap = {
@@ -70,6 +105,8 @@ in
     };
 
     users.groups.lidarr-mb-gap = {};
+    
+    programs.ssh.knownHosts = config.services.lidarr-mb-gap.sshKnownHosts;
 
     systemd.services.lidarr-mb-gap = {
       description = "Generate Lidarr MusicBrainz Gap Report";
@@ -96,7 +133,15 @@ in
           
           # Sync to VPS if enabled
           ${lib.optionalString (config.services.lidarr-mb-gap.syncToVPS && config.services.lidarr-mb-gap.vpsHost != null) ''
+            # Set up SSH options
+            SSH_OPTS=""
+            ${lib.optionalString (config.services.lidarr-mb-gap.sshKeyFile != null) ''
+              SSH_OPTS="-i ${config.services.lidarr-mb-gap.sshKeyFile}"
+            ''}
+            
+            # Use SSH options with rsync
             ${pkgs.rsync}/bin/rsync -avz --delete \
+              -e "ssh $SSH_OPTS -o StrictHostKeyChecking=yes" \
               ${config.services.lidarr-mb-gap.reportDir}/ \
               ${config.services.lidarr-mb-gap.vpsHost}:${config.services.lidarr-mb-gap.vpsPath}/
           ''}