feat(feedback): capture the browser UTC offset; Filed time in three zones

The account time zone defaults to UTC until a player saves a profile, so a
report's Filed time could only render in UTC even for a player clearly in
another zone. Capture the client's detected "±HH:MM" offset (browser_tz) with
each submission and show the Filed time in three zones in the operator console
— UTC, the browser offset detected at submit, and the sender's saved profile
zone — each shown "N/A" when not known, so the operator can tell what is
certainly known from what is merely defaulted.

- Thread browser_tz through the fbs envelope (+ Go/TS codegen), the gateway
  transcode + backend client, and the backend feedback service/store; add the
  column via migration 00004 (additive, image-rollback-safe).
- Fix fmtTimeIn to resolve "±HH:MM" offsets via account.ResolveZone;
  time.LoadLocation alone silently fell back to UTC for offset zones, which is
  the second reason a "+02:00" sender showed only UTC.
- Update ARCHITECTURE/FUNCTIONAL(+ru) docs and the feedback integration test.

backend/internal/feedback/service.go

@@ -72,7 +72,7 @@ func (svc *Service) SetNotifier(p notify.Publisher) {
 // validates the body (non-empty, within the rune limit) and the optional
 // attachment (size and extension allow-list). senderIP is the gateway-forwarded
 // client IP (validated); channel is the submitting platform.
-func (svc *Service) Submit(ctx context.Context, accountID uuid.UUID, body string, attachment []byte, attachmentName, channel, version, senderIP string) error {
+func (svc *Service) Submit(ctx context.Context, accountID uuid.UUID, body string, attachment []byte, attachmentName, channel, version, browserTZ, senderIP string) error {
 	acc, err := svc.accounts.GetByID(ctx, accountID)
 	if err != nil {
 		return err
@@ -112,9 +112,10 @@ func (svc *Service) Submit(ctx context.Context, accountID uuid.UUID, body string
 		attachmentName = "" // a name without bytes carries no attachment
 	}
 	ch := normalizeChannel(channel)
-	// Snapshot the sender's interface language and the client app version at submit time (acc
-	// is already loaded for the guest check) so the operator later sees the state as it was.
-	_, err = svc.store.Insert(ctx, accountID, body, attachment, attachmentName, ch, acc.PreferredLanguage, version, parseIP(senderIP))
+	// Snapshot the sender's interface language, the client app version and the client's
+	// detected UTC offset at submit time (acc is already loaded for the guest check) so the
+	// operator later sees the state as it was.
+	_, err = svc.store.Insert(ctx, accountID, body, attachment, attachmentName, ch, acc.PreferredLanguage, version, browserTZ, parseIP(senderIP))
 	return err
 }