fix: ensure theme toggle uses current theme value

Previously the theme toggle callback referenced nextTheme which was
computed at render time. Now it computes the new theme value inline
to avoid any potential stale closure issues.

Fixes #292

Author: Joel Klabo

apps/social/src/screens/SettingsScreen.tsx

@@ -68,12 +68,13 @@ export function SettingsScreen({
   const [profileError, setProfileError] = useState<string | null>(null);
 
   const handleThemeToggle = useCallback(() => {
-    setTheme(nextTheme);
+    const newTheme = theme === 'dark' ? 'light' : 'dark';
+    setTheme(newTheme);
     toast({
-      message: `Theme set to ${nextTheme}.`,
+      message: `Theme set to ${newTheme}.`,
       tone: 'success'
     });
-  }, [nextTheme, setTheme, toast]);
+  }, [theme, setTheme, toast]);
 
   const handleBrandPresetSelect = useCallback(
     (nextBrandPreset: NsBrandPreset) => {