refactor: migrate to modular tool-based architecture

- Implement tool registry system with individual tool modules
- Reorganize transformers into categorized source modules
- Remove emojiLibrary.js, consolidate into EmojiUtils and emojiData
- Fix mobile close button and tooltip functionality
- Add build system for transforms and emoji data
- Migrate from Python backend to pure JavaScript
- Add comprehensive documentation and testing
- Improve code organization and maintainability
- Ignore generated files (transforms-bundle.js, emojiData.js)

js/utils/theme.js

@@ -0,0 +1,37 @@
+window.ThemeUtils = {
+    toggleTheme(currentTheme) {
+        const newTheme = !currentTheme;
+        
+        if (newTheme) {
+            document.body.classList.add('dark-theme');
+            document.body.classList.remove('light-theme');
+        } else {
+            document.body.classList.add('light-theme');
+            document.body.classList.remove('dark-theme');
+        }
+        
+        try {
+            localStorage.setItem('theme', newTheme ? 'dark' : 'light');
+        } catch (e) {
+            console.warn('Failed to save theme preference:', e);
+        }
+        
+        return newTheme;
+    },
+    
+    initializeTheme() {
+        try {
+            const saved = localStorage.getItem('theme');
+            if (saved === 'light') {
+                return false;
+            } else if (saved === 'dark') {
+                return true;
+            }
+        } catch (e) {
+            console.warn('Failed to load theme preference:', e);
+        }
+        
+        return true;
+    }
+};
+