Refactor WireGuard secret paths for Linode configuration

- Updated secret paths in wireguard-linode.nix and configuration.nix to use 'linode' instead of 'wireguard' for clarity and consistency.
- Adjusted private key file references in wireguard.nix to align with the new secret path structure.

hosts/server/configuration.nix

@@ -37,7 +37,7 @@
       supportedFeatures = config.my.nix.features;
     }
   ];
-  sops.secrets."wireguard/server/private" = lib.mkIf config.my.secureHost {
+  sops.secrets."linode/server/private" = lib.mkIf config.my.secureHost {
     sopsFile = ../../secrets/wireguard.yaml;
   };
   networking = {
@@ -48,7 +48,7 @@
     };
     wireguard.interfaces.wg0 = lib.mkIf config.my.secureHost {
       ips = [ "${config.my.ips.wg-server}/32" ];
-      privateKeyFile = config.sops.secrets."wireguard/server/private".path;
+      privateKeyFile = config.sops.secrets."linode/server/private".path;
       peers = [
         {
           publicKey = "dFbiSekBwnZomarcS31o5+w6imHjMPNCipkfc2fZ3GY=";