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.

backend/internal/account/suspension_sweeper.go

@@ -0,0 +1,84 @@
+package account
+
+import (
+	"context"
+	"time"
+
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// suspensionSweepInterval is how often the sweeper re-checks for temporary blocks
+// that lapsed. A minute is well under the coarsest block grain (operators pick day
+// presets) while keeping the query trivial.
+const suspensionSweepInterval = time.Minute
+
+// suspensionExpiryQuerier is the slice of the account store the sweeper depends on:
+// the accounts whose temporary block lapsed in a window. *Store satisfies it; a fake
+// drives the sweeper's unit tests.
+type suspensionExpiryQuerier interface {
+	SuspensionsExpiredBetween(ctx context.Context, since, until time.Time) ([]uuid.UUID, error)
+}
+
+// SuspensionSweeper re-evaluates chat write access when a temporary block self-
+// expires. No operator action fires on expiry — the suspension gate just re-reads
+// the wall clock — so without this a temporarily blocked player would stay muted in
+// the moderated discussion chat after their block lapsed. Each tick it finds blocks
+// that expired since the previous tick and calls onExpire for the affected accounts;
+// onExpire is wired to publish the chat-access-changed event, after which the gateway
+// re-resolves the true eligibility. A liberal call (an account that still has another
+// active block) is therefore harmless. The window is in-memory, so a block that
+// expires while the process is down is not re-granted until the next operator action
+// or the player rejoins — an accepted best-effort gap.
+type SuspensionSweeper struct {
+	store    suspensionExpiryQuerier
+	onExpire func(accountID uuid.UUID)
+	log      *zap.Logger
+	// since is the upper bound of the previous swept window; the next sweep covers
+	// (since, now]. It advances only on a successful query, so a failed tick retries
+	// the same window rather than dropping expiries.
+	since time.Time
+}
+
+// NewSuspensionSweeper builds the sweeper over the account store, the per-account
+// expiry callback (publishing the chat-access-changed event) and a logger. The first
+// window opens at construction time, so blocks that lapsed earlier are not re-emitted.
+func NewSuspensionSweeper(store *Store, onExpire func(accountID uuid.UUID), log *zap.Logger) *SuspensionSweeper {
+	if log == nil {
+		log = zap.NewNop()
+	}
+	return &SuspensionSweeper{store: store, onExpire: onExpire, log: log, since: time.Now().UTC()}
+}
+
+// Interval reports the sweep cadence, for the startup log line.
+func (w *SuspensionSweeper) Interval() time.Duration { return suspensionSweepInterval }
+
+// Run sweeps every Interval until ctx is cancelled.
+func (w *SuspensionSweeper) Run(ctx context.Context) {
+	ticker := time.NewTicker(suspensionSweepInterval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			w.sweep(ctx)
+		}
+	}
+}
+
+// sweep emits a chat-access-changed signal for every account whose temporary block
+// lapsed in (since, now], then advances the window. On a query error it keeps the
+// window so the next tick retries it.
+func (w *SuspensionSweeper) sweep(ctx context.Context) {
+	now := time.Now().UTC()
+	ids, err := w.store.SuspensionsExpiredBetween(ctx, w.since, now)
+	if err != nil {
+		w.log.Warn("suspension expiry sweep failed", zap.Error(err))
+		return
+	}
+	w.since = now
+	for _, id := range ids {
+		w.onExpire(id)
+	}
+}