feat(feedback): capture the app version; show version + local Filed time

Each feedback submission now carries the client app version (__APP_VERSION__),
snapshotted like the interface language: FlatBuffers FeedbackSubmitRequest gains
a version field → gateway transcode → backend, persisted in a new nullable
feedback_messages.app_version column (migration 00003, additive so an image
rollback stays DB-safe). The operator console detail shows the app version and
renders the Filed time in UTC plus the sender's time zone (fmtTimeIn).

Touches: fbs schema + regenerated Go/TS codegen, codec + transport (the client
attaches its build), gateway transcode + backendclient, feedback store/service,
admin view + template, docs (ARCHITECTURE §15, FUNCTIONAL + _ru). Verified:
feedback integration tests (migration + version round-trip), codec round-trip,
check/unit/build green.

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, senderIP string) error {
+func (svc *Service) Submit(ctx context.Context, accountID uuid.UUID, body string, attachment []byte, attachmentName, channel, version, senderIP string) error {
 	acc, err := svc.accounts.GetByID(ctx, accountID)
 	if err != nil {
 		return err
@@ -112,9 +112,9 @@ 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 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, parseIP(senderIP))
+	// 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))
 	return err
 }