feat(telegram): promo bot + channel-chat moderation gate

Add a second standalone promo bot to the bot container (answers /start with a
localized message + a URL button into the main bot's Mini App) and gate write
access in a channel's linked discussion chat: grant on join when the Telegram
user is registered and neither admin-suspended nor holding a new chat_muted
role, and revoke/grant on the matching moderation change for a member currently
in the chat.

Eligibility (registered AND NOT suspended AND NOT chat_muted; the game
suspension dominates) is resolved once in the backend and reached two ways: the
bot's join-time unary ResolveChatEligibility over the existing mTLS bot-link,
and a backend chat_access_changed event -> gateway -> ChatGate command
(idempotent; a temporary-block-expiry sweeper may over-emit). The bot guards the
block/unblock path with getChatMember, since bots cannot list members.

A web_app button cannot open another bot's Mini App (it signs initData with the
sending bot's token), so the promo button is a t.me ?startapp URL reusing the
UI's VITE_TELEGRAM_LINK. The bot must be a chat admin with the restrict-members
right and chat_member in its allowed updates.

No schema change: chat_muted reuses the data-driven account_roles table.

docs/FUNCTIONAL.md

@@ -33,7 +33,10 @@ App** launch authenticates from the platform's signed `initData`, themes the UI
 the Telegram colours, and — on first contact — seeds the new account's interface
 language from the Telegram client. Telegram runs a **single bot**: every player uses
 the same bot, and all of its chat and out-of-app notifications are written in the
-player's own **interface language** (en/ru). Guests are session-only with restricted features
+player's own **interface language** (en/ru). A separate optional **promo bot** can run alongside the
+main one — its only job is to answer `/start` with a short message and a button that opens the
+**main** bot's app, where the player picks their game variant; it is an onboarding entry point that
+touches nothing else. Guests are session-only with restricted features
 (auto-match only; no friends, stats or history); an abandoned guest that never
 joined a game and has been idle past the retention window is garbage-collected. While the app is open the client
 keeps a live stream and receives in-app updates in real time — the opponent's move,
@@ -320,6 +323,14 @@ plus the reason when one was given, and the app stops all background traffic wit
 temporary block lifts itself when it expires; the operator can also **unblock** from the user card
 at any time (games already lost stay lost).
 
+Where the bot manages a channel's **linked discussion chat**, only a **registered** player who is
+**not blocked** may write there: the bot grants the right to write when such a player joins, while an
+unregistered or blocked one stays muted (the promo bot points newcomers at the game so they register).
+An operator can also **mute a player in the chat only** — a `chat_muted` role on the user card —
+without a full account block; an account block mutes them in the chat regardless. Muting/unmuting and
+blocking/unblocking take effect for a player already in the chat; one who is not in it is unaffected
+until they next join.
+
 From the user card the operator can also **top up a player's hint wallet**: an additive grant
 (1–100 hints per action) that raises the balance shown on the card. Grants are **raise-only** —
 the console can never lower a wallet (a player only loses hints by spending them in a game), so an