feat(ui): per-kind active-game limit lock on the New Game screen

Carry the caller's per-tier active-game caps and each game's kind on the
wire (Profile.game_limits + GameView.kind, additive FBS + gateway transcode
+ client codec, committed regen). The New Game screen counts the player's
active games per kind from the lobby and locks a capped start: an outline
button with a lock that opens a funnel modal instead of a game -- a sign-in
prompt for a guest, a "finish a current game first" notice for a signed-in
account (native Telegram popup, in-app modal elsewhere). The lock lifts via
the existing profile refetch after a guest->durable upgrade.

Remove the lobby's old at_game_limit New-Game tab disable + notice: the flag
(now the random-kind cap) conflicted with the per-kind lock -- it hid the
screen where the lock lives and wrongly blocked an unfulfilled kind. The New
Game tab is always enabled; the per-kind start lock is the only gate. The
at_game_limit wire field stays (unused by the client) for a later cleanup.

Tests: client lock logic + codec kind/game_limits roundtrip + gateway
transcode encode + native popup builders (unit); a mock e2e for the lock
badge and the modal.

pkg/fbs/scrabblefb/GameView.go

@@ -209,8 +209,20 @@ func (rcv *GameView) MutateUnreadMessages(n bool) bool {
 	return rcv._tab.MutateBoolSlot(32, n)
 }
 
+func (rcv *GameView) Kind() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(34))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *GameView) MutateKind(n int32) bool {
+	return rcv._tab.MutateInt32Slot(34, n)
+}
+
 func GameViewStart(builder *flatbuffers.Builder) {
-	builder.StartObject(15)
+	builder.StartObject(16)
 }
 func GameViewAddId(builder *flatbuffers.Builder, id flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(id), 0)
@@ -260,6 +272,9 @@ func GameViewAddUnreadChat(builder *flatbuffers.Builder, unreadChat bool) {
 func GameViewAddUnreadMessages(builder *flatbuffers.Builder, unreadMessages bool) {
 	builder.PrependBoolSlot(14, unreadMessages, false)
 }
+func GameViewAddKind(builder *flatbuffers.Builder, kind int32) {
+	builder.PrependInt32Slot(15, kind, 0)
+}
 func GameViewEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }