Stage 11: account linking & merge (email + Telegram Login Widget)

Link an email (confirm-code) or Telegram (web Login Widget) to the current
account; if the identity already has its own account, merge the two into the
one in use (the current account is primary, except a guest initiator whose
durable counterpart wins). The merge runs in one transaction
(internal/accountmerge): stats + hint wallet summed, paid_account ORed,
identities/games/chat/complaints transferred, friends/blocks de-duplicated,
the secondary kept as a merged_into tombstone so a shared finished game's
no-cascade FKs hold; a shared active game blocks the merge.

- migration 00009: accounts.paid_account, merged_into, merged_at (+ jetgen)
- internal/link orchestrator; session.RevokeAllForAccount on merge
- connector ValidateLoginWidget RPC + loginwidget HMAC validator
- edge ops link.email.request/confirm/merge, link.telegram.confirm/merge;
  supersedes the Stage 8 email.bind.* surface (request never reveals 'taken'
  before the code is verified, so a probe cannot enumerate addresses)
- UI Profile link section + irreversible-merge dialog; Telegram web sign-in
- focused regression tests (merge core, guest inversion, active-game refusal,
  finished-shared-game kept), gateway transcode + connector + UI codec/e2e
- docs: PLAN, ARCHITECTURE 3/4/9, FUNCTIONAL(+ru), module READMEs

platform/telegram/README.md

@@ -30,8 +30,12 @@ Telegram-specific.
 
 ## gRPC API
 
-`pkg/proto/telegram/v1`, service `Telegram`: `ValidateInitData`, `Notify`,
-`SendToUser`, `SendToGameChannel`. Generated Go is committed under `pkg`.
+`pkg/proto/telegram/v1`, service `Telegram`: `ValidateInitData`,
+`ValidateLoginWidget`, `Notify`, `SendToUser`, `SendToGameChannel`. Generated Go is
+committed under `pkg`. `ValidateLoginWidget` (Stage 11) verifies Telegram **Login
+Widget** web sign-in data — HMAC under `SHA-256(bot_token)`, distinct from initData
+(`internal/loginwidget`) — for attaching a Telegram identity to an account from a
+browser.
 
 ## Deep-link scheme