refactor: standardize config structure and consolidate modules

- Standardized apps/ directory by renaming all entry points (e.g., home.nix) to default.nix and updating imports to use directory paths.
- Consolidated system/ logic into modules/system/, eliminating the top-level system/ directory and redundant wrappers.
- Merged subsidiary utility scripts (e.g., hakase-popup.nix, switch-wallpaper.nix) into their parent default.nix files for better cohesion.
- Cleaned up unused files and updated all module references to reflect the new structure.

apps/hypridle/default.nix

@@ -0,0 +1,30 @@
+{ pkgs, ... }:
+{
+  services.hypridle = {
+    enable = true;
+    settings = {
+      general = {
+        after_sleep_cmd = "hyprctl dispatch dpms on";
+        ignore_dbus_inhibit = false;
+        lock_cmd = "hyprlock";
+        before_sleep_cmd = "loginctl lock-session"; # lock before suspend
+      };
+
+      listener = [
+        {
+          timeout = 300; # 5min
+          on-timeout = "loginctl lock-session"; # lock screen when timeout has passed
+        }
+        {
+          timeout = 330; # 5.5min
+          on-timeout = "hyprctl dispatch dpms off"; # screen off when timeout has passed
+          on-resume = "hyprctl dispatch dpms on"; # screen on when activity is detected after timeout has passed
+        }
+        {
+          timeout = 1800; # 30min
+          on-timeout = "systemctl suspend"; # suspend pc
+        }
+      ];
+    };
+  };
+}