v1.0.1: Add comprehensive theme switcher and fix dark mode issues

- Add theme switcher widget with Auto/Light/Dark options in header
- Implement manual theme override system with localStorage persistence
- Add complete button theme overrides for all variants (primary, outline-*)
- Fix missing focus states and placeholder colors for light theme
- Add proper alert styling for both themes
- Fix expression input error state colors in dark theme
- Complete comprehensive theme coverage for all UI elements
- Theme switcher overrides CSS media queries when manually selected
- All buttons, inputs, and surfaces now properly adapt to theme changes

src/index.css

@@ -92,4 +92,26 @@ code {
 .result-output {
   background-color: #e7f3ff;
   border-color: #b3d7ff;
+}
+
+/* Dark mode support for error states */
+@media (prefers-color-scheme: dark) {
+  .error {
+    background-color: #4a1e1e !important;
+    border-color: #6d2c2c !important;
+    color: #f8d7da !important;
+  }
+}
+
+/* Manual theme overrides for error states */
+.theme-dark .error {
+  background-color: #4a1e1e !important;
+  border-color: #6d2c2c !important;
+  color: #f8d7da !important;
+}
+
+.theme-light .error {
+  background-color: #f8d7da !important;
+  border-color: #f5c6cb !important;
+  color: #721c24 !important;
 }