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.

backend/internal/inttest/admin_test.go

@@ -4,7 +4,6 @@ package inttest
 
 import (
 	"context"
-	"errors"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -280,76 +279,6 @@ func TestConsoleThrottledViewAndFlagClear(t *testing.T) {
 	}
 }
 
-// TestConsoleGrantHints drives the admin hint-wallet grant end to end: the card shows the form,
-// the action is CSRF-guarded, a same-origin grant adds to the wallet, a second grant adds again
-// (rather than replacing), the inclusive per-grant cap is accepted, and an out-of-range or
-// non-numeric amount is refused without changing the balance.
-func TestConsoleGrantHints(t *testing.T) {
-	ctx := context.Background()
-	accounts := account.NewStore(testDB)
-	id := provisionAccount(t)
-	srv := server.New(":0", server.Deps{
-		Logger: zap.NewNop(), Accounts: accounts, Games: newGameService(), Registry: testRegistry, DictDir: dictDir(),
-	})
-	h := srv.Handler()
-	base := "http://admin.test/_gm/users/" + id.String()
-
-	if code, body := consoleDo(h, http.MethodGet, base, "", ""); code != http.StatusOK || !strings.Contains(body, "Add hints") {
-		t.Fatalf("user card = %d, has grant form = %v", code, strings.Contains(body, "Add hints"))
-	}
-	// The grant POST is CSRF-guarded like every console action.
-	if code, _ := consoleDo(h, http.MethodPost, base+"/grant-hints", "amount=5", ""); code != http.StatusForbidden {
-		t.Fatalf("grant without origin = %d, want 403", code)
-	}
-	// A same-origin grant adds to the wallet.
-	if code, body := consoleDo(h, http.MethodPost, base+"/grant-hints", "amount=5", "http://admin.test"); code != http.StatusOK || !strings.Contains(body, "now 5") {
-		t.Fatalf("grant 5 = %d, body has 'now 5' = %v", code, strings.Contains(body, "now 5"))
-	}
-	if acc, err := accounts.GetByID(ctx, id); err != nil || acc.HintBalance != 5 {
-		t.Fatalf("after grant 5: balance=%d err=%v, want 5", acc.HintBalance, err)
-	}
-	// A second grant adds again rather than replacing.
-	if code, body := consoleDo(h, http.MethodPost, base+"/grant-hints", "amount=3", "http://admin.test"); code != http.StatusOK || !strings.Contains(body, "now 8") {
-		t.Fatalf("grant 3 = %d, body has 'now 8' = %v", code, strings.Contains(body, "now 8"))
-	}
-	// An out-of-range or non-numeric amount is refused; the balance is left untouched.
-	for _, bad := range []string{"0", "-1", "101", "x", ""} {
-		if code, body := consoleDo(h, http.MethodPost, base+"/grant-hints", "amount="+bad, "http://admin.test"); code != http.StatusOK || !strings.Contains(body, "Invalid amount") {
-			t.Fatalf("grant %q = %d, has 'Invalid amount' = %v", bad, code, strings.Contains(body, "Invalid amount"))
-		}
-	}
-	if acc, err := accounts.GetByID(ctx, id); err != nil || acc.HintBalance != 8 {
-		t.Fatalf("after invalid grants: balance=%d err=%v, want 8", acc.HintBalance, err)
-	}
-	// The inclusive per-grant cap (100) is accepted.
-	if code, _ := consoleDo(h, http.MethodPost, base+"/grant-hints", "amount=100", "http://admin.test"); code != http.StatusOK {
-		t.Fatalf("grant 100 = %d, want 200", code)
-	}
-	if acc, err := accounts.GetByID(ctx, id); err != nil || acc.HintBalance != 108 {
-		t.Fatalf("after grant 100: balance=%d err=%v, want 108", acc.HintBalance, err)
-	}
-}
-
-// TestGrantHintsStore covers the wallet store method directly: an additive grant raises the
-// balance, a non-positive grant is rejected, and an unknown account yields ErrNotFound.
-func TestGrantHintsStore(t *testing.T) {
-	ctx := context.Background()
-	accounts := account.NewStore(testDB)
-	id := provisionAccount(t)
-	if bal, err := accounts.GrantHints(ctx, id, 4); err != nil || bal != 4 {
-		t.Fatalf("grant 4 = (%d, %v), want (4, nil)", bal, err)
-	}
-	if bal, err := accounts.GrantHints(ctx, id, 6); err != nil || bal != 10 {
-		t.Fatalf("grant 6 = (%d, %v), want (10, nil)", bal, err)
-	}
-	if _, err := accounts.GrantHints(ctx, id, 0); err == nil {
-		t.Error("grant 0 should be rejected (non-positive)")
-	}
-	if _, err := accounts.GrantHints(ctx, uuid.New(), 1); !errors.Is(err, account.ErrNotFound) {
-		t.Errorf("grant unknown account = %v, want ErrNotFound", err)
-	}
-}
-
 // consoleDo issues a request to h, optionally with an Origin header, and returns
 // the status and body. Form bodies are sent as application/x-www-form-urlencoded.
 func consoleDo(h http.Handler, method, target, body, origin string) (int, string) {