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.

docs/launcher-menu.md

@@ -79,7 +79,7 @@ its option is set and reverted by its unpatch when unset:
   sounds and controller navigation keep working;
 - `show-all/`: empties the list Steam hides without Developer Mode.
 
-Their anchors (APIs, React props, CSS) are in `modules/lib/signatures.json`
+Their anchors (APIs, React props, CSS) are in `modules/steam-ui-patches/lib/signatures.json`
 and verified by the [offline checker](ui-patches.md#after-a-steam-update).
 
 ## Hidden apps