Refactor: Simplify module structure and reorganize services

- Removed system/ directory, merged applications into users/geir.nix
- Simplified fonts.nix to bare minimum (users can add more)
- Moved transmission.nix to sleeper-service/services/ (machine-specific)
- Organized grey-area services into services/ directory
- Updated import paths and tested all configurations
- Added research documentation for deploy-rs and GNU Stow

machines/grey-area/services/calibre-web.nix

@@ -0,0 +1,16 @@
+{ config, pkgs, ... }:
+{
+  services.calibre-web = {
+    enable = true;
+    group = "users";
+    listen = {
+        ip = "0.0.0.0";
+        port = 8083;
+    };
+    options = {
+      calibreLibrary = "/mnt/remote/media/books/calibre/";
+      enableBookUploading = true;
+    };
+  };
+  networking.firewall.allowedTCPPorts = [ 8083 ];
+}