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.

modules/system/kernel.nix

@@ -0,0 +1,13 @@
+{pkgs, ...}: {
+  boot = {
+    kernelPackages = pkgs.linuxPackages_cachyos; # from chaotic input
+    kernelParams = [
+      "quiet"
+      "splash"
+      "intremap=on"
+      "boot.shell_on_fail"
+      "udev.log_priority=3"
+      "rd.systemd.show_status=auto"
+    ];
+  };
+}