feat(feedback): in-app user feedback with admin review and account roles

User-facing Feedback screen (Settings -> Info, registered accounts only): a
message (<=1024 runes) plus one optional attachment, an anti-spam gate (one
unreviewed message at a time), and the operator's inline reply with a
Settings/Info badge. Server-rendered admin console section (/_gm/feedback):
unread/read/archived queue with per-user search, detail with read/reply/
archive/delete/delete-all, safe attachment serving (nosniff, images inline via
<img>, others download-only). Introduces account_roles, the first per-account
role table; feedback_banned blocks only feedback submission, granted/revoked
from /users and the delete-with-block action.

- migration 00004_feedback (feedback_messages + account_roles) + jetgen
- backend internal/feedback (store+service), internal/account/roles.go
- wire: FlatBuffers feedback.submit/get/unread; gateway guest gate (Op.NonGuest,
  is_guest via session resolve) -> guest_forbidden before any backend call
- reply push reuses NotificationEvent with a new admin_reply sub-kind
- UI: /feedback route + screen, attachment picker, badge, channel detection, i18n
- tests: feedback unit (Go+UI), gateway guest-gate, inttest lifecycle, e2e
- docs: PLAN stage 19, ARCHITECTURE s15, FUNCTIONAL(+ru), TESTING, READMEs

backend/cmd/backend/main.go

@@ -22,6 +22,7 @@ import (
 	"scrabble/backend/internal/config"
 	"scrabble/backend/internal/connector"
 	"scrabble/backend/internal/engine"
+	"scrabble/backend/internal/feedback"
 	"scrabble/backend/internal/game"
 	"scrabble/backend/internal/link"
 	"scrabble/backend/internal/lobby"
@@ -167,6 +168,8 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	socialSvc := social.NewService(social.NewStore(db), accounts, games)
 	socialSvc.SetNotifier(hub)
 	socialSvc.SetMetrics(tel.MeterProvider().Meter("scrabble/backend/social"))
+	feedbackSvc := feedback.NewService(feedback.NewStore(db), accounts)
+	feedbackSvc.SetNotifier(hub)
 
 	// Robot opponent: provision its durable account pool (a hard startup
 	// dependency, like the dictionaries) and start its move driver. The matchmaker
@@ -202,6 +205,7 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		Sessions:      sessions,
 		Accounts:      accounts,
 		Games:         games,
+		Feedback:      feedbackSvc,
 		Social:        socialSvc,
 		Matchmaker:    matchmaker,
 		Invitations:   invitations,