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.

scripts/vr-keyboard-replay.mjs

@@ -1,7 +1,8 @@
 // Replays recorded swipes (window.__sfuiSwipePaths of Steam's SharedJSContext,
 // saved as JSON) through the decoder: top candidates and the cost terms of
 // the expected word. The dictionary is the built vr-keyboard-dictionary.js.
-// usage: node scripts/vr-keyboard-replay.mjs modules/vr-keyboard/decoder.js <dictionary.js> <paths.json> [word]
+// usage: node scripts/vr-keyboard-replay.mjs modules/vr-keyboard/swipe-decoder.js
+//          <dictionary.js> <paths.json> [word]
 import { readFileSync } from 'node:fs';
 const [, , decoderPath, dictPath, pathsPath, expected] = process.argv;
 const D = (0, eval)(readFileSync(decoderPath, 'utf8'));