Switch repo to English, add i18n with EN/DE language files and first-start language selection

- in-game texts moved to lang/en.lang and lang/de.lang (key = text, placeholders)
- game logic emits message keys + args, translated at display time
- localStorage access via own miniquad JS plugin (www/dc_plugin.js)
- code comments, DESIGN.md, CREDITS.md translated; README.md added

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.cargo/config.toml

@@ -1,4 +1,4 @@
-# quad-snd (macroquad-Audio) importiert JS-Funktionen aus mq_js_bundle.js.
-# Neuere Rust-Versionen verlangen dafür explizit --allow-undefined.
+# quad-snd (macroquad audio) imports JS functions from mq_js_bundle.js, and our own
+# plugin (www/dc_plugin.js) provides more. Newer Rust versions need --allow-undefined for that.
 [target.wasm32-unknown-unknown]
 rustflags = ["-C", "link-arg=--allow-undefined"]