feat(profile): carry linked identities in the profile (email, telegram, vk)

Add email / telegram_linked / vk_linked to the Profile (fbs table + regenerated
Go/TS bindings, gateway ProfileResp + encodeProfile, backend DTO, UI model +
decode). They are filled outside the pure projection — Server.profileResponse now
reads the account's identities (like the banner seam) — and will drive the profile's
Add / Unlink / change-email controls.

ui/src/lib/mock/data.ts

@@ -39,6 +39,9 @@ export const PROFILE: Profile = {
   notificationsInAppOnly: true,
   // Every variant enabled, so the mock-driven UI offers the full New Game picker.
   variantPreferences: ['erudit_ru', 'scrabble_ru', 'scrabble_en'],
+  email: 'you@example.com',
+  telegramLinked: false,
+  vkLinked: false,
 };
 
 // Seed social/account data for the mock (pnpm start + Playwright). The mock profile