feat: unify language handling across the application

- Updated the language configuration to use a single source of truth from `DEFAULT_LANGUAGE` for the bot, API, and Mini App, eliminating auto-detection from user settings.
- Refactored the `get_lang` function to always return `DEFAULT_LANGUAGE`, ensuring consistent language usage throughout the application.
- Modified the handling of language in various components, including API responses and UI elements, to reflect the new language management approach.
- Enhanced documentation and comments to clarify the changes in language handling.
- Added unit tests to verify the new language handling behavior and ensure coverage for the updated functionality.

webapp/js/auth.js

@@ -34,23 +34,15 @@ export function getInitData() {
   if (hash) {
     const fromHash = getTgWebAppDataFromHash(hash);
     if (fromHash) return fromHash;
-    try {
-      const hashParams = new URLSearchParams(hash);
-      const tgFromHash = hashParams.get("tgWebAppData");
-      if (tgFromHash) return decodeURIComponent(tgFromHash);
-    } catch (e) {
-      /* ignore */
-    }
+    const hashParams = new URLSearchParams(hash);
+    const tgFromHash = hashParams.get("tgWebAppData");
+    if (tgFromHash) return tgFromHash;
   }
   const q = window.location.search
     ? new URLSearchParams(window.location.search).get("tgWebAppData")
     : null;
   if (q) {
-    try {
-      return decodeURIComponent(q);
-    } catch (e) {
-      return q;
-    }
+    return q;
   }
   return "";
 }