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>

src/main.rs

@@ -2,7 +2,9 @@
 
 mod game;
 mod gfx;
+mod i18n;
 mod map;
+mod platform;
 mod render3d;
 mod sound;
 mod ui;
@@ -59,6 +61,11 @@ async fn main() {
     let mut seed = (miniquad::date::now() * 1000.0) as u32 | 1;
     let (mut game, mut cam) = new_game(seed);
     let mut ui = Ui::new();
+    // language: stored choice, otherwise ask on first start
+    match platform::storage_get("dc.lang") {
+        Some(code) if i18n::set_language(&code) => {}
+        _ => ui.show_langsel = true,
+    }
     let mut inp = Input { ldown: None, rdown: None, rlast: (0.0, 0.0), rdrag: false, mlast: None, minimap_drag: false };
 
     loop {
@@ -234,6 +241,12 @@ async fn main() {
                     (game, cam) = new_game(seed);
                     ui.show_help = false;
                 }
+                UiAction::SelectLanguage(code) => {
+                    i18n::set_language(&code);
+                    platform::storage_set("dc.lang", &code);
+                    ui.show_langsel = false;
+                    game.sfx_ui(game::Sfx::Click);
+                }
                 UiAction::Consumed => {}
                 UiAction::None => {
                     if game.state == 0 {