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/DEPLOYMENT.md

@@ -34,6 +34,13 @@ Add the module to your NixOS configuration. You have two options:
     syncToVPS = true;
     vpsHost = "user@vps";  # Your SSH host alias
     vpsPath = "/var/www/html";
+    sshKeyFile = "/var/lib/lidarr-mb-gap/.ssh/id_ed25519";
+    sshKnownHosts = {
+      vps = {
+        hostNames = [ "vps" "vps.example.com" ];
+        publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...";  # Get from ssh-keyscan
+      };
+    };
   };
 }
 ```
@@ -62,6 +69,18 @@ Add the module to your NixOS configuration. You have two options:
           services.lidarr-mb-gap.reportDir = "/var/lib/lidarr-mb-gap/reports";
           services.lidarr-mb-gap.envFile = "/var/lib/lidarr-mb-gap/.env";
           services.lidarr-mb-gap.runInterval = "daily";
+          
+          # Optional: SSH configuration for VPS sync
+          services.lidarr-mb-gap.syncToVPS = true;
+          services.lidarr-mb-gap.vpsHost = "user@vps";
+          services.lidarr-mb-gap.vpsPath = "/var/www/html";
+          services.lidarr-mb-gap.sshKeyFile = "/var/lib/lidarr-mb-gap/.ssh/id_ed25519";
+          services.lidarr-mb-gap.sshKnownHosts = {
+            vps = {
+              hostNames = [ "vps" "vps.example.com" ];
+              publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...";
+            };
+          };
         }
         ./configuration.nix
       ];
@@ -100,20 +119,96 @@ sudo chmod 600 /var/lib/lidarr-mb-gap/.env
 
 ### 3. Configure SSH for rsync (if using auto-sync)
 
-If you enabled `syncToVPS`, set up SSH key authentication:
+If you enabled `syncToVPS`, you need to set up SSH key authentication for the `lidarr-mb-gap` user.
+
+#### Step 1: Generate SSH Key Pair
 
 ```bash
-# On the server
-ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_lidarr
-ssh-copy-id -i ~/.ssh/id_ed25519_lidarr.pub user@vps
+# Generate a dedicated SSH key for the service
+sudo -u lidarr-mb-gap ssh-keygen -t ed25519 -f /var/lib/lidarr-mb-gap/.ssh/id_ed25519 -N ""
 
-# Add to ~/.ssh/config
-Host vps
-    HostName your-vps-ip-or-domain
-    User your-username
-    IdentityFile ~/.ssh/id_ed25519_lidarr
+# Or generate as your user and copy it
+ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_lidarr -N ""
+sudo mkdir -p /var/lib/lidarr-mb-gap/.ssh
+sudo cp ~/.ssh/id_ed25519_lidarr /var/lib/lidarr-mb-gap/.ssh/id_ed25519
+sudo cp ~/.ssh/id_ed25519_lidarr.pub /var/lib/lidarr-mb-gap/.ssh/id_ed25519.pub
+sudo chown -R lidarr-mb-gap:lidarr-mb-gap /var/lib/lidarr-mb-gap/.ssh
+sudo chmod 600 /var/lib/lidarr-mb-gap/.ssh/id_ed25519
+sudo chmod 644 /var/lib/lidarr-mb-gap/.ssh/id_ed25519.pub
 ```
 
+#### Step 2: Add Public Key to VPS
+
+```bash
+# Copy the public key to your VPS
+sudo -u lidarr-mb-gap cat /var/lib/lidarr-mb-gap/.ssh/id_ed25519.pub | ssh user@vps "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
+
+# Or manually:
+# 1. Display the public key:
+sudo -u lidarr-mb-gap cat /var/lib/lidarr-mb-gap/.ssh/id_ed25519.pub
+
+# 2. On your VPS, add it to ~/.ssh/authorized_keys (or the target user's authorized_keys)
+```
+
+#### Step 3: Get VPS Host Key (for known_hosts)
+
+```bash
+# Get the VPS host key fingerprint
+ssh-keyscan -t ed25519 your-vps-hostname-or-ip
+
+# This will output something like:
+# your-vps-hostname ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...
+```
+
+#### Step 4: Configure in NixOS
+
+Add SSH configuration to your NixOS config:
+
+```nix
+services.lidarr-mb-gap = {
+  enable = true;
+  # ... other options ...
+  
+  syncToVPS = true;
+  vpsHost = "user@vps-hostname";  # or "user@vps.example.com"
+  vpsPath = "/var/www/html";
+  
+  # Path to SSH private key (optional, defaults to ~/.ssh/id_ed25519)
+  sshKeyFile = "/var/lib/lidarr-mb-gap/.ssh/id_ed25519";
+  
+  # SSH known hosts (prevents host key verification prompts)
+  sshKnownHosts = {
+    vps = {
+      hostNames = [ "vps-hostname" "vps.example.com" "1.2.3.4" ];  # All possible hostnames/IPs
+      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...";  # From ssh-keyscan output
+    };
+  };
+};
+```
+
+**Alternative: Manual Setup (if not using NixOS config)**
+
+If you prefer to set up SSH keys manually without NixOS configuration:
+
+```bash
+# The service will use default SSH key location: /var/lib/lidarr-mb-gap/.ssh/id_ed25519
+# Just ensure the key exists and is properly configured
+```
+
+#### Step 5: Test SSH Connection
+
+Before enabling the service, test that SSH works:
+
+```bash
+# Test SSH connection as the service user
+sudo -u lidarr-mb-gap ssh -i /var/lib/lidarr-mb-gap/.ssh/id_ed25519 user@vps "echo 'SSH connection successful'"
+
+# Or if using default key location:
+sudo -u lidarr-mb-gap ssh user@vps "echo 'SSH connection successful'"
+```
+
+If this works, rsync should work too. If you get host key verification errors, make sure you've configured `sshKnownHosts` in your NixOS config.
+
 ### 4. Build and Switch
 
 ```bash