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/scrabble.fbs

@@ -330,12 +330,11 @@ table StateView {
   bag_len:int;
   hints_remaining:int;
   alphabet:[AlphabetEntry];
-  // wallet_balance is the requesting player's global hint-wallet balance, sent apart from
-  // hints_remaining (which folds the wallet in with the per-game allowance) so the client can
-  // separate the two: the per-game allowance remaining is hints_remaining - wallet_balance, and
-  // the wallet is a single global figure the client keeps live across games (added trailing —
-  // backward-compatible).
-  wallet_balance:int;
+  // wallet_balance is deprecated (D31): the purchasable hint wallet moved to the profile (payments),
+  // and hints_remaining now carries the per-game allowance alone. The field is tombstoned rather than
+  // deleted so the vtable slots of the fields after it stay stable across a rolling deploy (an old
+  // SPA served before the deploy must keep reading a new gateway correctly). No accessor is generated.
+  wallet_balance:int (deprecated);
   // hint_unlock_left_seconds is, for a vs_ai game, how many seconds until the idle hint unlocks
   // (the robot's last move plus the idle window, computed from the SERVER clock online / the device
   // clock offline, capped at the window and floored at 0); 0 for a human's first move (no robot move
@@ -393,10 +392,9 @@ table ComplaintRequest {
   note:string;
 }
 
-// HintResult is the top-ranked move plus the remaining hint budget. wallet_balance is the
-// global hint-wallet balance after spending (see StateView.wallet_balance), so the client
-// refreshes its live wallet and re-derives the per-game allowance (added trailing —
-// backward-compatible).
+// HintResult is the top-ranked move plus hints_remaining (the per-game allowance alone) and
+// wallet_balance (the purchasable hint wallet after spending, from payments). The client adopts
+// wallet_balance into the profile so the badge stays live across games (see lib/hints).
 table HintResult {
   move:MoveRecord;
   hints_remaining:int;

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)
 }