Update masApps and add Homebrew shell initialization

Convert masApps from list to set for better structure consistency. Add initialization for Homebrew in the Fish shell to ensure the environment is correctly set up.

modules/darwin/system/homebrew/default.nix

@@ -39,5 +39,8 @@ in
       # With mutableTaps disabled, taps can no longer be added imperatively with `brew tap`.
       mutableTaps = false;
     };
+    programs.fish.shellInit = ''
+      /opt/homebrew/bin/brew shellenv | source
+    '';
   };
 }

systems/aarch64-darwin/m4/default.nix

@@ -9,7 +9,7 @@ with lib.metacfg;
       "libusb"
       "mas"
     ];
-    masApps = [ ];
+    masApps = { };
   };
 
   metacfg = {