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>

Dockerfile

@@ -4,18 +4,19 @@ RUN rustup target add wasm32-unknown-unknown
 WORKDIR /src
 COPY Cargo.toml Cargo.lock ./
 COPY .cargo .cargo
-# Abhängigkeiten vorab bauen (Docker-Cache)
+# build dependencies first (Docker layer cache)
 RUN mkdir src && echo "fn main() {}" > src/main.rs \
  && cargo build --release --target wasm32-unknown-unknown \
  && rm -rf src
 COPY assets assets
+COPY lang lang
 COPY src src
 RUN touch src/main.rs && cargo build --release --target wasm32-unknown-unknown \
  && mkdir /out \
  && cp target/wasm32-unknown-unknown/release/dungeoncraft.wasm /out/ \
  && cp "$CARGO_HOME"/registry/src/*/macroquad-*/js/mq_js_bundle.js /out/
 
-# --- Auslieferung: nginx
+# --- serve: nginx
 FROM nginx:alpine
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 COPY www/ /usr/share/nginx/html/