feat(admin): manual account blocking (suspensions)

Operator-driven hard block, the counterpart to the soft high-rate flag: permanent or until a date, with an optional reason chosen from an editable en+ru picklist (snapshotted onto the block). A block forfeits the player's active games (opponent wins, as a resignation) and cancels their open matchmaking games. A backend gate refuses a blocked account on every /api/v1/user/* route except the block-status probe with 403 account_blocked, which threads through the gateway as the Execute result_code; the UI surfaces it as a terminal blocked screen and stops all push/poll. Temporary blocks self-expire; the operator can unblock at any time (lost games stay lost). Sessions are not revoked, so the blocked client can still reach the exempt block-status endpoint.

Backend: migration 00003 (account_suspensions + suspension_reasons) + jet regen; account suspension store; game.ForfeitAllForAccount; requireNotSuspended gate + block-status endpoint; admin console block/unblock + Reasons CRUD. Wire: fbs BlockStatus + account.block_status gateway op. UI: blocked screen, app state, transport/codec, i18n. Docs: ARCHITECTURE, FUNCTIONAL(+ru), PRERELEASE (AB).

backend/internal/server/handlers.go

@@ -46,6 +46,9 @@ func (s *Server) registerRoutes() {
 		u.GET("/profile", s.handleProfile)
 		u.PUT("/profile", s.handleUpdateProfile)
 		u.GET("/stats", s.handleStats)
+		// Exempt from the suspension gate (see requireNotSuspended): the one endpoint a blocked
+		// client may still reach, to fetch the block's expiry and reason for the blocked screen.
+		u.GET("/block-status", s.handleBlockStatus)
 	}
 	if s.links != nil {
 		// Account linking & merge. The request step always mails a code;