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/server/handlers_admin_console.go

@@ -29,10 +29,6 @@ import (
 // adminPageSize is the page size of the admin console's paginated lists.
 const adminPageSize = 50
 
-// maxHintGrant caps a single operator hint grant. Grants are additive and can never lower a
-// wallet, so a fat-fingered grant cannot be undone through this form; the cap bounds one mistake.
-const maxHintGrant = 100
-
 // registerConsole mounts the server-rendered admin console under /_gm. The gateway
 // puts HTTP Basic-Auth in front of /_gm and reverse-proxies it verbatim; the
 // backend trusts the gateway (as for all of /api) and adds only a same-origin guard
@@ -56,7 +52,6 @@ func (s *Server) registerConsole(router *gin.Engine) {
 	gm.GET("/users/:id", s.consoleUserDetail)
 	gm.POST("/users/:id/message", s.consoleUserMessage)
 	gm.POST("/users/:id/clear-high-rate-flag", s.consoleClearHighRateFlag)
-	gm.POST("/users/:id/grant-hints", s.consoleGrantHints)
 	gm.POST("/users/:id/block", s.consoleBlockUser)
 	gm.POST("/users/:id/unblock", s.consoleUnblockUser)
 	gm.POST("/users/:id/grant-role", s.consoleGrantRole)
@@ -354,7 +349,6 @@ func (s *Server) consoleUserDetail(c *gin.Context) {
 	view := adminconsole.UserDetailView{
 		ID: acc.ID.String(), DisplayName: acc.DisplayName, Language: acc.PreferredLanguage,
 		TimeZone: acc.TimeZone, Guest: acc.IsGuest, NotificationsInAppOnly: acc.NotificationsInAppOnly,
-		PaidAccount: acc.PaidAccount, HintBalance: acc.HintBalance, HintGrantMax: maxHintGrant,
 		CreatedAt: fmtTime(acc.CreatedAt), HasStats: !acc.IsGuest, ConnectorEnabled: s.connector != nil,
 	}
 	if acc.MergedInto != uuid.Nil {
@@ -963,30 +957,6 @@ func (s *Server) consoleClearHighRateFlag(c *gin.Context) {
 	s.renderConsoleMessage(c, "Cleared", "high-rate flag cleared", "/_gm/users/"+id.String())
 }
 
-// consoleGrantHints adds hints to a user's wallet. The grant is additive (raise-only): it tops a
-// player up and can never lower what they already hold, so blocking a reduction is inherent rather
-// than a separate guard. A single grant is bounded by maxHintGrant.
-func (s *Server) consoleGrantHints(c *gin.Context) {
-	id, ok := s.consoleUUID(c, "/_gm/users")
-	if !ok {
-		return
-	}
-	back := "/_gm/users/" + id.String()
-	n, err := strconv.Atoi(trimForm(c, "amount"))
-	if err != nil || n < 1 || n > maxHintGrant {
-		s.renderConsoleMessage(c, "Invalid amount", fmt.Sprintf("enter a whole number of hints to add, between 1 and %d", maxHintGrant), back)
-		return
-	}
-	balance, err := s.accounts.GrantHints(c.Request.Context(), id, n)
-	if err != nil {
-		s.consoleError(c, err)
-		return
-	}
-	// A non-empty hint wallet removes the banner: nudge an open client to re-check.
-	s.publishBannerChange(id)
-	s.renderConsoleMessage(c, "Granted", fmt.Sprintf("added %d hint(s); the wallet is now %d", n, balance), back)
-}
-
 // consoleRemoveEmail deletes the account's bound email identity (and any pending
 // confirmations), freeing the address. It refuses to remove the account's only
 // identity, which would leave it unreachable.