Clearer file names and layout; docs/development.md

- steam-keyboard-patch.nix -> vr-keyboard-extra-keys.nix (option
  keyboard.vr.extraKeys), helper.mjs -> xdotool-helper.mjs;
  homeManagerModules.steam-keyboard-patch stays as an alias.
- vr-keyboard: panel.js/unpatch-panel.js/relay.mjs ->
  suggestions-panel/{patch,unpatch}.js + relay.mjs; decoder.js ->
  swipe-decoder.js; build.nix split into dictionary.nix and check.nix.
- modules/lib -> modules/steam-ui-patches/lib (the UI patch library).
- docs/development.md: repository layout (what runs where), runtime names.

Patch names, user services and state files are unchanged.

modules/launcher-menu.nix

@@ -22,7 +22,7 @@
 { config, lib, pkgs, ... }:
 let
   cfg = config.steamFrame.launcherMenu;
-  inherit (import ./lib { inherit pkgs; }) mkPatch;
+  inherit (import ./steam-ui-patches/lib { inherit pkgs; }) mkPatch;
   sharedJSContext = { title = "SharedJSContext"; };
 
   iconSuggest = pkgs.writeShellApplication {