Add zoxide integration for smart directory navigation

- Add zoxide package to flake.nix
- Enable zoxide with zsh integration in modules/zsh.nix
- Configure zoxide to replace cd command with smart frecency-based navigation
- Add zi alias for interactive directory selection with fzf

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

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

flake.nix

@@ -74,6 +74,7 @@
         git-credential-oauth
         rsync
         gnumake
+        zoxide
       ];
 
       fonts.fontconfig.enable = true;