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

flake.lock

@@ -969,6 +969,7 @@
         "skills-anthropic": "skills-anthropic",
         "skills-basecamp": "skills-basecamp",
         "skills-kestra": "skills-kestra",
+        "skills-superpowers": "skills-superpowers",
         "skills-vercel": "skills-vercel"
       }
     },
@@ -1040,6 +1041,22 @@
         "type": "github"
       }
     },
+    "skills-superpowers": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1776996157,
+        "narHash": "sha256-0WupTacT1jIwVBloj1i0RF7wIllVtP8eMPRl7VrXdbE=",
+        "owner": "obra",
+        "repo": "superpowers",
+        "rev": "6efe32c9e2dd002d0c394e861e0529675d1ab32e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "obra",
+        "repo": "superpowers",
+        "type": "github"
+      }
+    },
     "skills-vercel": {
       "flake": false,
       "locked": {