feat(ads): VK post-move interstitial + retire deprecated hint_balance/paid_account

Interstitial video after a confirmed play or a hint, VK-only, offline
banner-only. The gate is client-mirrored: the backend puts the config
cooldowns (global 5m / vs_ai 30m / hint 1m) and a suppressed flag (the
no-ads / no_banner gate, same as the banner) on Profile.ads via adsFor;
the client self-gates on a per-kind last-shown time in localStorage, with
the VITE_ADS_STUB contour "ad fired" toast. Never fires after a pass,
exchange or resign. maybeShowInterstitial + vkShowInterstitial; the codec
and gateway transcode carry the ads block.

Also retires the deprecated accounts.hint_balance / paid_account domain
usage (expand-contract, code only — the columns stay for a later DROP so
image rollback stays DB-safe): drop the Account fields and their scan, the
dead account.SpendHint, account.GrantHints and the admin grant-hints
action; the in-game hint display now comes wholly from the payments hint
benefit. Banner eligibility and account merge no longer read the legacy
flags.

Tests: ads.test.ts (the client-mirrored gate), the codec ads round-trip,
the gateway ads transcode test, and a profile ads-config integration test
(cooldowns + suppressed under no-ads / no_banner). Docs: PAYMENTS §10 (+ru)
interstitial, the decision amends, backend README, the plan.

pkg/fbs/scrabble.fbs

@@ -264,6 +264,18 @@ table Profile {
   // preload the right dictionary and pin a new local game without a separate request (added
   // trailing — backward-compatible).
   dict_versions:[DictVersion];
+  // ads carries the post-move interstitial config (cooldowns + suppressed) for the client-mirrored
+  // gate (added trailing — backward-compatible).
+  ads:AdsInfo;
+}
+
+// AdsInfo is the post-move interstitial config: the client-mirrored cooldowns (seconds) and whether
+// ads are suppressed in the caller's context (a no-ads benefit here, or the no_banner role).
+table AdsInfo {
+  cooldown_global_s:int;
+  cooldown_vs_ai_s:int;
+  cooldown_hint_s:int;
+  suppressed:bool;
 }
 
 // BlockStatus reports the caller's current manual block. The UI fetches it after any operation

pkg/fbs/scrabblefb/AdsInfo.go

@@ -0,0 +1,109 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type AdsInfo struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsAdsInfo(buf []byte, offset flatbuffers.UOffsetT) *AdsInfo {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &AdsInfo{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishAdsInfoBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsAdsInfo(buf []byte, offset flatbuffers.UOffsetT) *AdsInfo {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &AdsInfo{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedAdsInfoBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *AdsInfo) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *AdsInfo) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *AdsInfo) CooldownGlobalS() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *AdsInfo) MutateCooldownGlobalS(n int32) bool {
+	return rcv._tab.MutateInt32Slot(4, n)
+}
+
+func (rcv *AdsInfo) CooldownVsAiS() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *AdsInfo) MutateCooldownVsAiS(n int32) bool {
+	return rcv._tab.MutateInt32Slot(6, n)
+}
+
+func (rcv *AdsInfo) CooldownHintS() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *AdsInfo) MutateCooldownHintS(n int32) bool {
+	return rcv._tab.MutateInt32Slot(8, n)
+}
+
+func (rcv *AdsInfo) Suppressed() bool {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
+	if o != 0 {
+		return rcv._tab.GetBool(o + rcv._tab.Pos)
+	}
+	return false
+}
+
+func (rcv *AdsInfo) MutateSuppressed(n bool) bool {
+	return rcv._tab.MutateBoolSlot(10, n)
+}
+
+func AdsInfoStart(builder *flatbuffers.Builder) {
+	builder.StartObject(4)
+}
+func AdsInfoAddCooldownGlobalS(builder *flatbuffers.Builder, cooldownGlobalS int32) {
+	builder.PrependInt32Slot(0, cooldownGlobalS, 0)
+}
+func AdsInfoAddCooldownVsAiS(builder *flatbuffers.Builder, cooldownVsAiS int32) {
+	builder.PrependInt32Slot(1, cooldownVsAiS, 0)
+}
+func AdsInfoAddCooldownHintS(builder *flatbuffers.Builder, cooldownHintS int32) {
+	builder.PrependInt32Slot(2, cooldownHintS, 0)
+}
+func AdsInfoAddSuppressed(builder *flatbuffers.Builder, suppressed bool) {
+	builder.PrependBoolSlot(3, suppressed, false)
+}
+func AdsInfoEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}

pkg/fbs/scrabblefb/Profile.go

@@ -231,8 +231,21 @@ func (rcv *Profile) DictVersionsLength() int {
 	return 0
 }
 
+func (rcv *Profile) Ads(obj *AdsInfo) *AdsInfo {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(38))
+	if o != 0 {
+		x := rcv._tab.Indirect(o + rcv._tab.Pos)
+		if obj == nil {
+			obj = new(AdsInfo)
+		}
+		obj.Init(rcv._tab.Bytes, x)
+		return obj
+	}
+	return nil
+}
+
 func ProfileStart(builder *flatbuffers.Builder) {
-	builder.StartObject(17)
+	builder.StartObject(18)
 }
 func ProfileAddUserId(builder *flatbuffers.Builder, userId flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(userId), 0)
@@ -291,6 +304,9 @@ func ProfileAddDictVersions(builder *flatbuffers.Builder, dictVersions flatbuffe
 func ProfileStartDictVersionsVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
 	return builder.StartVector(4, numElems, 4)
 }
+func ProfileAddAds(builder *flatbuffers.Builder, ads flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(17, flatbuffers.UOffsetT(ads), 0)
+}
 func ProfileEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }