fix: code review fixes

- Fix hardcoded user path in webapps.nix (use homeDirectory)
- Normalize wallpapers option to use .enable suffix
- Remove duplicate FZF keybind declaration
- Update comments to match actual implementation

home/features/coding/default.nix

@@ -23,6 +23,7 @@ in {
         src = inputs.skills-anthropic;
         selectSkills = ["pdf" "docx" "frontend-design"];
       }
+      {src = inputs.skills-superpowers;}
       {src = inputs.skills-vercel;}
       {src = inputs.skills-basecamp;}
       {src = inputs.skills-kestra;}