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.

pkg/fbs/scrabble.fbs

@@ -383,6 +383,7 @@ table FeedbackSubmitRequest {
   attachment:[ubyte];
   attachment_name:string;
   channel:string;
+  version:string;
 }
 
 // FeedbackReply is the operator's answer shown back to the player.

pkg/fbs/scrabblefb/FeedbackSubmitRequest.go

@@ -99,8 +99,16 @@ func (rcv *FeedbackSubmitRequest) Channel() []byte {
 	return nil
 }
 
+func (rcv *FeedbackSubmitRequest) Version() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(12))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
 func FeedbackSubmitRequestStart(builder *flatbuffers.Builder) {
-	builder.StartObject(4)
+	builder.StartObject(5)
 }
 func FeedbackSubmitRequestAddBody(builder *flatbuffers.Builder, body flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(body), 0)
@@ -117,6 +125,9 @@ func FeedbackSubmitRequestAddAttachmentName(builder *flatbuffers.Builder, attach
 func FeedbackSubmitRequestAddChannel(builder *flatbuffers.Builder, channel flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(3, flatbuffers.UOffsetT(channel), 0)
 }
+func FeedbackSubmitRequestAddVersion(builder *flatbuffers.Builder, version flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(4, flatbuffers.UOffsetT(version), 0)
+}
 func FeedbackSubmitRequestEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }