feat: Full UI internationalization, pool hashrate stats, and layout caching

- Replace all hardcoded English strings with TR() translation keys across
  every tab, dialog, and component (~20 UI files)
- Expand all 8 language files (de, es, fr, ja, ko, pt, ru, zh) with
  complete translations (~37k lines added)
- Improve i18n loader with exe-relative path fallback and English base
  fallback for missing keys
- Add pool-side hashrate polling via pool stats API in xmrig_manager
- Introduce Layout::beginFrame() per-frame caching and refresh balance
  layout config only on schema generation change
- Offload daemon output parsing to worker thread
- Add CJK subset fallback font for Chinese/Japanese/Korean glyphs

src/ui/schema/ui_schema.h

@@ -255,8 +255,12 @@ public:
 
     /**
      * @brief Look up a DrawList custom element style
+     *
+     * Returns a cached const reference. The cache is invalidated on
+     * hot-reload (applyIfDirty) and full loads. For missing elements
+     * a static empty sentinel is returned.
      */
-    DrawElementStyle drawElement(const std::string& section, const std::string& name) const;
+    const DrawElementStyle& drawElement(const std::string& section, const std::string& name) const;
 
     /**
      * @brief Find a raw stored element by section and name.
@@ -365,6 +369,10 @@ private:
         std::any data;  // holds toml::table at runtime
     };
     std::unordered_map<std::string, StoredElement> elements_;
+
+    // Parsed DrawElementStyle cache — avoids repeated TOML table iteration.
+    // Populated lazily on first drawElement() lookup, cleared on reload.
+    mutable std::unordered_map<std::string, DrawElementStyle> styleCache_;
 };
 
 // Convenience alias