feat: share UserProfileContainer between /mypage and /users/:id

[zigzagdev]

Summary

• Extract UserProfileContainer (accepts id: number as a prop): owns the get/update/delete hooks, immediate-reflection state, and renders UserProfileView — this is the shared implementation
• UserGetContainer (/users/:id) becomes a thin wrapper: reads id from the route param, passes it through
• MyPageContainer (/mypage) becomes a thin wrapper: reads id from useAuth().user.id (the authenticated user's own id), passes it through
• No URL redirect — /mypage stays /mypage, it just renders the same component tree as viewing your own /users/:id
• Removes the standalone logout button that was on the /mypage placeholder (tracked separately, not re-added here)
• Tests reorganized to match: detailed behavior tests moved to user-profile-container.test.tsx; user-get-container.test.tsx and the new mypage-container.test.tsx only verify each wrapper passes the right id through

Related

Closes #468

Test plan

• npx tsc --noEmit
• npx jest (206 tests)
• npm run format:check
• npm run build

[zigzagdev]

OK