Replace deprecated xorg.* package set references (eval warnings on nixpkgs 26.05+)

[MichaelFisher1997]

Consumers of this flake get 10 evaluation warnings on every build against nixpkgs 26.05+:

evaluation warning: The xorg package set has been deprecated, 'xorg.libX11' has been renamed to 'libx11'
evaluation warning: The xorg package set has been deprecated, 'xorg.libXcomposite' has been renamed to 'libxcomposite'
evaluation warning: The xorg package set has been deprecated, 'xorg.libXdamage' has been renamed to 'libxdamage'
evaluation warning: The xorg package set has been deprecated, 'xorg.libXext' has been renamed to 'libxext'
evaluation warning: The xorg package set has been deprecated, 'xorg.libXfixes' has been renamed to 'libxfixes'
evaluation warning: The xorg package set has been deprecated, 'xorg.libXrandr' has been renamed to 'libxrandr'
evaluation warning: The xorg package set has been deprecated, 'xorg.libxcb' has been renamed to 'libxcb'

Location: flake.nix lines 95-101 (the Electron wrapper buildInputs).

Fix: replace with the top-level attrs — all verified present in nixpkgs 26.05:

-              xorg.libX11
-              xorg.libXcomposite
-              xorg.libXdamage
-              xorg.libXext
-              xorg.libXfixes
-              xorg.libXrandr
-              xorg.libxcb
+              libx11
+              libxcomposite
+              libxdamage
+              libxext
+              libxfixes
+              libxrandr
+              libxcb

(found while auditing the home-manager config that consumes this flake)