fix(i18n): reject format-incompatible translations

Many strings are used directly as printf/ImGui format strings, and translations
are loaded from user/installer-modifiable JSON with no validation. A translated
value that drops or changes a conversion specifier would be passed to printf with
mismatched varargs (undefined behavior) on a wallet screen.

overlayTranslations() now compares each translated value's argument signature
against the English source and keeps English on mismatch. Also adds the
send_status_unconfirmed string used by the deferred-send-result path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.h

@@ -7,6 +7,7 @@
 #include <string>
 #include <unordered_map>
 #include <vector>
+#include <nlohmann/json_fwd.hpp>
 
 namespace dragonx {
 namespace util {
@@ -58,7 +59,12 @@ public:
 private:
     I18n();
     void loadBuiltinEnglish();
-    
+    // Overlay translated strings onto the English base, but reject any value whose printf
+    // format-specifier signature differs from the English source (keep English instead).
+    // Many strings are used directly as printf/ImGui format strings, so a mismatched
+    // translation (dropped/changed specifier) is undefined behavior — this prevents it.
+    void overlayTranslations(const nlohmann::json& translations);
+
     std::string current_locale_ = "en";
     std::unordered_map<std::string, std::string> strings_;
     std::vector<std::pair<std::string, std::string>> available_languages_;