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

pkg/README.md

@@ -16,6 +16,8 @@ fbs/scrabblefb/   # committed generated Go for the schema
 - **`proto/push/v1`** is the single gRPC server-stream the backend exposes and
   the gateway subscribes to (`Event{user_id, kind, payload, event_id}`); the
   `payload` is an opaque FlatBuffers body the gateway forwards verbatim.
+- **`proto/telegram/v1`** is the Telegram connector's RPC contract (Stage 9; Stage 11
+  added `ValidateLoginWidget` for the web Login Widget sign-in).
 - **`fbs`** holds the client↔gateway request/response and event payloads as
   FlatBuffers tables. The backend encodes the push payloads from these types; the
   gateway transcodes the rest to and from the backend's JSON; the UI generates