feat: Add weather foreground option (experimental)

- Add weatherEffectsForeground setting to render weather effects in front of chat
- Add UI toggle in main panel (visible when Dynamic Weather toggle is visible)
- Apply z-index 9998 when foreground option is enabled
- Fix weather container sizing with viewport units (100vh/100dvh) for better mobile support

src/systems/ui/weatherEffects.js

@@ -270,6 +270,11 @@ export function updateWeatherEffect() {
     }
 
     if (weatherContainer) {
+        // Apply foreground z-index if experimental setting is enabled
+        if (extensionSettings.weatherEffectsForeground) {
+            weatherContainer.style.zIndex = '9998';
+        }
+
         document.body.appendChild(weatherContainer);
     }
 }