fix: resolve TypeScript strict mode violations in ProfileMenu MainSection

Fix two strict violations in ProfileMenu/sections/MainSection.tsx introduced
by the main branch merge:
- Access user?.username safely since user can be undefined
- Replace .filter(Boolean) with type predicate to narrow array type correctly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: github-actions[bot]

packages/shared/src/components/ProfileMenu/sections/MainSection.tsx

@@ -2,6 +2,7 @@ import React from 'react';
 import type { ReactElement } from 'react';
 
 import { ProfileSection } from '../ProfileSection';
+import type { ProfileSectionItemProps } from '../ProfileSectionItem';
 import {
   AnalyticsIcon,
   CoinIcon,
@@ -22,7 +23,7 @@ export const MainSection = (): ReactElement => {
       items={[
         {
           title: 'Your profile',
-          href: `${webappUrl}${user.username}`,
+          href: `${webappUrl}${user?.username}`,
           icon: UserIcon,
         },
         hasAccessToCores && {
@@ -32,7 +33,7 @@ export const MainSection = (): ReactElement => {
         },
         {
           title: 'Achievements',
-          href: `${webappUrl}${user.username}/achievements`,
+          href: `${webappUrl}${user?.username}/achievements`,
           icon: MedalBadgeIcon,
         },
         {
@@ -45,7 +46,7 @@ export const MainSection = (): ReactElement => {
           href: `${webappUrl}analytics`,
           icon: AnalyticsIcon,
         },
-      ].filter(Boolean)}
+      ].filter((item): item is ProfileSectionItemProps => !!item)}
     />
   );
 };