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>

www/dc_plugin.js

@@ -0,0 +1,32 @@
+// DungeonCraft browser plugin for miniquad: localStorage access for the Rust code.
+(function () {
+    "use strict";
+    var pending = null;
+
+    function bytes(ptr, len) {
+        return new Uint8Array(wasm_memory.buffer, ptr, len);
+    }
+    function str(ptr, len) {
+        return new TextDecoder().decode(bytes(ptr, len));
+    }
+
+    function register(importObject) {
+        importObject.env.dc_storage_get = function (kp, kl) {
+            var v = null;
+            try { v = window.localStorage.getItem(str(kp, kl)); } catch (e) { }
+            if (v === null) { pending = null; return -1; }
+            pending = new TextEncoder().encode(v);
+            return pending.length;
+        };
+        importObject.env.dc_storage_take = function (ptr) {
+            if (pending === null) return;
+            bytes(ptr, pending.length).set(pending);
+            pending = null;
+        };
+        importObject.env.dc_storage_set = function (kp, kl, vp, vl) {
+            try { window.localStorage.setItem(str(kp, kl), str(vp, vl)); } catch (e) { }
+        };
+    }
+
+    miniquad_add_plugin({ register_plugin: register, version: 1, name: "dungeoncraft" });
+})();