fix: flatten home configs into packages to satisfy flake schema

The previous fix exposed `.activationPackage` but still nested them under
`packages.<system>.homeConfigurations`, which is an attrset, not a derivation.

`nix flake check` requires EVERY attribute under `packages.<system>` to be
a derivation. Now flattening home configurations directly into packages with
the prefix `homeConfigurations-<name>` to ensure each is a top-level derivation.

Changes:
- Merge pipe result directly with `//` instead of nesting under `homeConfigurations`
- Prefix each home config with "homeConfigurations-" to avoid naming conflicts

Result: `packages.x86_64-linux.homeConfigurations-user` instead of
        `packages.x86_64-linux.homeConfigurations.user`

snowfall-lib/flake/default.nix

@@ -223,16 +223,19 @@ let
         // (builtins.listToAttrs (
           builtins.map (system: {
             name = system;
-            value = flake-outputs.packages.${system} // {
-              homeConfigurations = pipe homes [
+            value =
+              flake-outputs.packages.${system}
+              // (pipe homes [
                 (filterAttrs (_: home: home.system == system))
                 (mapAttrs (home-name: _: flake-outputs.homeConfigurations.${home-name}.activationPackage))
                 (mapAttrs' (
                   name: value:
-                  nameValuePair (if hasSuffix "@${system}" name then removeSuffix "@${system}" name else name) value
+                  nameValuePair (
+                    "homeConfigurations-"
+                    + (if hasSuffix "@${system}" name then removeSuffix "@${system}" name else name)
+                  ) value
                 ))
-              ];
-            };
+              ]);
           }) (builtins.attrNames flake-outputs.pkgs)
         ));
     };