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.

gateway/internal/backendclient/api.go

@@ -37,6 +37,11 @@ type ProfileResp struct {
 	// Banner is the advertising-banner block, present only for a viewer eligible to
 	// see the banner. The gateway forwards it verbatim into the Profile payload.
 	Banner *BannerResp `json:"banner,omitempty"`
+	// Email is the confirmed email ("" when none); TelegramLinked/VkLinked report an
+	// attached platform identity — they drive the profile's link/unlink/change controls.
+	Email          string `json:"email"`
+	TelegramLinked bool   `json:"telegram_linked"`
+	VkLinked       bool   `json:"vk_linked"`
 }
 
 // BannerResp is the advertising-banner block of an eligible viewer's profile: the