refactor(modules): rename system/ to nixos/

Clearer naming to distinguish NixOS system modules from
Home Manager modules (nixos/ vs home/).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -26,7 +26,7 @@ This is a modular, flake-based NixOS configuration for a single host (`hakase`).
 ### Module Organization
 
 **Two-tier module system:**
-- `modules/system/` - NixOS system-level modules (boot, kernel, services, hardware)
+- `modules/nixos/` - NixOS system-level modules (boot, kernel, services, hardware)
 - `modules/home/` - Home Manager user-level modules (imported via `home/hakase.nix`)
 
 **Application configs:** Each application has its own directory in `apps/` with a `default.nix` and optional sub-modules (e.g., `apps/hyprland/hypr/*.nix` for Hyprland settings).
@@ -37,7 +37,7 @@ This is a modular, flake-based NixOS configuration for a single host (`hakase`).
 flake.nix
   └─ nixosConfigurations.hakase
        ├─ hosts/hakase/configuration.nix
-       │   └─ modules/system/default.nix (imports all system modules)
+       │   └─ modules/nixos/default.nix (imports all system modules)
        └─ home-manager
            └─ home/hakase.nix
                └─ modules/home/* → apps/*