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/platform.rs

@@ -0,0 +1,50 @@
+// Browser integration via our own miniquad JS plugin (www/dc_plugin.js):
+// persistent key/value storage (localStorage). Native builds use an in-memory fallback.
+
+#[cfg(target_arch = "wasm32")]
+mod imp {
+    extern "C" {
+        fn dc_storage_get(key: *const u8, key_len: u32) -> i32;
+        fn dc_storage_take(dst: *mut u8);
+        fn dc_storage_set(key: *const u8, key_len: u32, val: *const u8, val_len: u32);
+    }
+
+    pub fn storage_get(key: &str) -> Option<String> {
+        unsafe {
+            let n = dc_storage_get(key.as_ptr(), key.len() as u32);
+            if n < 0 {
+                return None;
+            }
+            let mut buf = vec![0u8; n as usize];
+            dc_storage_take(buf.as_mut_ptr());
+            String::from_utf8(buf).ok()
+        }
+    }
+
+    pub fn storage_set(key: &str, val: &str) {
+        unsafe { dc_storage_set(key.as_ptr(), key.len() as u32, val.as_ptr(), val.len() as u32) }
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+mod imp {
+    use std::cell::RefCell;
+    use std::collections::HashMap;
+    thread_local! {
+        static STORE: RefCell<HashMap<String, String>> = RefCell::new(HashMap::new());
+    }
+    pub fn storage_get(key: &str) -> Option<String> {
+        STORE.with(|s| s.borrow().get(key).cloned())
+    }
+    pub fn storage_set(key: &str, val: &str) {
+        STORE.with(|s| s.borrow_mut().insert(key.to_string(), val.to_string()));
+    }
+}
+
+pub use imp::*;
+
+// Lets the JS plugin loader know this crate uses the "dungeoncraft" plugin
+#[no_mangle]
+pub extern "C" fn dungeoncraft_crate_version() -> u32 {
+    1
+}