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.

backend/internal/server/dto.go

@@ -56,6 +56,13 @@ type profileResponse struct {
 	// see the banner (a free account with an empty hint wallet and without the
 	// no_banner role), absent otherwise. See banner.go.
 	Banner *bannerDTO `json:"banner,omitempty"`
+	// Email is the account's confirmed email address ("" when none); TelegramLinked and
+	// VkLinked report whether a platform identity is attached. They drive the profile's
+	// link / unlink / change-email controls, and are filled outside the pure projection
+	// (they read the account's identities). See Server.profileResponse.
+	Email          string `json:"email"`
+	TelegramLinked bool   `json:"telegram_linked"`
+	VkLinked       bool   `json:"vk_linked"`
 }
 
 // tileDTO is one placed (or to-place) tile.