feat(configurations)!: flatten down, introduce meta.nix

Flatten down directory structure:
- From: `./hosts/${configuration-type}/${system}/{configuration,deploy}.nix`
-   To: `./hosts/${configuration-type}/{meta,configuration}.nix`
Keep `system` and `deploy-rs` config in `meta.nix`
Update `flake.lock`

hosts/nixos/jeeves/transmission.nix

@@ -0,0 +1,31 @@
+{ lib, pkgs, config, ... }:
+{
+  environment.systemPackages = with pkgs; [
+    tremc
+  ];
+
+  services = {
+    transmission = {
+      enable = true;
+      package = pkgs.transmission_4;
+      openRPCPort = true;
+      webHome = pkgs.flood-for-transmission;
+      # TODO: `credentialsFile` for RPC password with agenix
+      settings = {
+        download-dir = "/data/torrents/download";
+        incomplete-dir = "/data/torrents/incomplete";
+        incomplete-dir-enabled = true;
+        rpc-bind-address = "0.0.0.0";
+        rpc-whitelist = "127.0.0.1,192.168.*.*,10.100.0.*,*.local";
+      };
+    };
+
+    nginx = {
+      virtualHosts."transmission.jeeves.local" = {
+        enableACME = false;
+        forceSSL = false;
+        locations."/".proxyPass = "http://127.0.0.1:9091";
+      };
+    };
+  };
+}