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/wire/build.go

@@ -92,7 +92,6 @@ type StateView struct {
 	Rack                  []int
 	BagLen                int
 	HintsRemaining        int
-	WalletBalance         int
 	HintUnlockLeftSeconds int
 	Alphabet              []AlphabetEntry
 }
@@ -256,7 +255,6 @@ func BuildStateView(b *flatbuffers.Builder, s StateView) flatbuffers.UOffsetT {
 	fb.StateViewAddRack(b, rack)
 	fb.StateViewAddBagLen(b, int32(s.BagLen))
 	fb.StateViewAddHintsRemaining(b, int32(s.HintsRemaining))
-	fb.StateViewAddWalletBalance(b, int32(s.WalletBalance))
 	fb.StateViewAddHintUnlockLeftSeconds(b, int32(s.HintUnlockLeftSeconds))
 	if hasAlphabet {
 		fb.StateViewAddAlphabet(b, alphabet)