fix(game): show granted/bought hints in-game — finish the D31 wire removal

The in-game hint badge ignored the payments hint wallet: loading a game clobbered
app.profile.hintBalance with the deprecated StateView.wallet_balance (zeroed in the
D31 domain removal but left in the protocol as a dead 0, then synced over the real
balance at game load).

Finish the removal honestly. StateView carries the per-game allowance alone
(hints_remaining); the purchasable wallet lives solely on the profile and the client
adds it (lib/hints). Removed StateView.wallet_balance across every layer — backend
StateView/DTO, notify.PlayerState (live events), gateway StateResp + wire.StateView,
the client model/codec/mock/localgame — and dropped the now-unused wallet arg from
hintsRemaining. The FBS field is tombstoned `(deprecated)` (not deleted) so the vtable
slots after it stay stable across a rolling deploy; no accessor is generated. HintResult
keeps wallet_balance (the real post-spend payments balance the client adopts into the
profile). The StateView type no longer has walletBalance, so the clobber cannot return
without a compile error.

Tests: hintsRemaining (2-arg); hints.hintsLeft (allowance + live wallet, no strip); the
game state/hint integration (allowance-only HintsRemaining); gateway transcode; FBS regen.

pkg/fbs/scrabblefb/StateView.go

@@ -144,18 +144,6 @@ func (rcv *StateView) AlphabetLength() int {
 	return 0
 }
 
-func (rcv *StateView) WalletBalance() int32 {
-	o := flatbuffers.UOffsetT(rcv._tab.Offset(16))
-	if o != 0 {
-		return rcv._tab.GetInt32(o + rcv._tab.Pos)
-	}
-	return 0
-}
-
-func (rcv *StateView) MutateWalletBalance(n int32) bool {
-	return rcv._tab.MutateInt32Slot(16, n)
-}
-
 func (rcv *StateView) HintUnlockLeftSeconds() int32 {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(18))
 	if o != 0 {
@@ -195,9 +183,6 @@ func StateViewAddAlphabet(builder *flatbuffers.Builder, alphabet flatbuffers.UOf
 func StateViewStartAlphabetVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
 	return builder.StartVector(4, numElems, 4)
 }
-func StateViewAddWalletBalance(builder *flatbuffers.Builder, walletBalance int32) {
-	builder.PrependInt32Slot(6, walletBalance, 0)
-}
 func StateViewAddHintUnlockLeftSeconds(builder *flatbuffers.Builder, hintUnlockLeftSeconds int32) {
 	builder.PrependInt32Slot(7, hintUnlockLeftSeconds, 0)
 }