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/internal/server/server.go

@@ -21,6 +21,7 @@ import (
 	"scrabble/backend/internal/adminconsole"
 	"scrabble/backend/internal/connector"
 	"scrabble/backend/internal/engine"
+	"scrabble/backend/internal/feedback"
 	"scrabble/backend/internal/game"
 	"scrabble/backend/internal/link"
 	"scrabble/backend/internal/lobby"
@@ -54,6 +55,9 @@ type Deps struct {
 	Sessions *session.Service
 	Accounts *account.Store
 	Games    *game.Service
+	// Feedback is the user-feedback domain service (the /api/v1/user/feedback
+	// endpoints and the console section). A nil Feedback disables them.
+	Feedback *feedback.Service
 	// Social, Matchmaker, Invitations and Emails are the domain services
 	// the REST handlers route to.
 	Social      *social.Service
@@ -91,6 +95,7 @@ type Server struct {
 	sessions    *session.Service
 	accounts    *account.Store
 	games       *game.Service
+	feedback    *feedback.Service
 	social      *social.Service
 	matchmaker  *lobby.Matchmaker
 	invitations *lobby.InvitationService
@@ -132,6 +137,7 @@ func New(addr string, deps Deps) *Server {
 		sessions:      deps.Sessions,
 		accounts:      deps.Accounts,
 		games:         deps.Games,
+		feedback:      deps.Feedback,
 		social:        deps.Social,
 		matchmaker:    deps.Matchmaker,
 		invitations:   deps.Invitations,