style: align comments with the project conventions

Apply a codebase-wide comment audit against the comment conventions:
split banned semicolons and multi-sentence lines into one sentence per
line, cut cross-file and history narration, trim file-top headers to a
single purpose line, and drop verbosity that did not earn its place.
Prose docs (CLAUDE.md, install.md) get the same one-sentence-per-line
and no-semicolon treatment.

modules/desktop/portals.nix

@@ -10,8 +10,9 @@ in
   config = lib.mkIf cfg.enable {
     # The backend packages arrive with the compositor, so only the routing is set
     # here.
-    # GTK is the default backend, and the three compositor-native requests go to
-    # Hyprland.
+    # Screen sharing, screenshots, and global shortcuts need the compositor's
+    # own backend.
+    # Everything else uses GTK.
     xdg.portal.config.common = {
       default = [ "gtk" ];
       "org.freedesktop.impl.portal.ScreenCast" = [ "hyprland" ];