Reorganize configuration into modular directory structure

- Create modules/ directory for Nix configuration modules
- Create config/ directory for configuration files
- Move nvim.nix, tmux.nix, zsh.nix to modules/
- Move p10k.zsh to config/
- Update flake.nix import paths to reference new structure
- Update zsh.nix p10k.zsh path reference
- Update README.md architecture documentation
- Keep tmux.sh at root for easy accessibility

This provides better separation between Nix modules and config files
while maintaining a clean, scalable structure.

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

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

flake.nix

@@ -30,9 +30,9 @@
     homeConfiguration = { pkgs, ... }: {
       imports = [ 
         nixvim.homeManagerModules.nixvim
-        ./nvim.nix 
-        ./tmux.nix 
-        ./zsh.nix 
+        ./modules/nvim.nix 
+        ./modules/tmux.nix 
+        ./modules/zsh.nix 
       ];
 
       home.username = "yanlin";