🎨 chore(web): apply ESLint and Prettier auto-fixes (baseline)

- Ran: bun run eslint:fix && bun run lint:fix
- Inserted AGPL license header via eslint-plugin-header
- Enforced no-multiple-empty-lines and other lint rules
- Formatted code using Prettier v3 (@so1ve/prettier-config)
- No functional changes; formatting-only baseline across JS/JSX files

web/src/hooks/common/useHeaderBar.js

@@ -109,16 +109,25 @@ export const useHeaderBar = ({ onMobileMenuToggle, drawerOpen }) => {
     navigate('/login');
   }, [navigate, t, userDispatch]);
 
-  const handleLanguageChange = useCallback((lang) => {
-    i18n.changeLanguage(lang);
-  }, [i18n]);
+  const handleLanguageChange = useCallback(
+    (lang) => {
+      i18n.changeLanguage(lang);
+    },
+    [i18n],
+  );
 
-  const handleThemeToggle = useCallback((newTheme) => {
-    if (!newTheme || (newTheme !== 'light' && newTheme !== 'dark' && newTheme !== 'auto')) {
-      return;
-    }
-    setTheme(newTheme);
-  }, [setTheme]);
+  const handleThemeToggle = useCallback(
+    (newTheme) => {
+      if (
+        !newTheme ||
+        (newTheme !== 'light' && newTheme !== 'dark' && newTheme !== 'auto')
+      ) {
+        return;
+      }
+      setTheme(newTheme);
+    },
+    [setTheme],
+  );
 
   const handleMobileMenuToggle = useCallback(() => {
     if (isMobile) {