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.

ui/src/gen/fbs/scrabblefb/feedback-submit-request.ts

@@ -63,8 +63,15 @@ version(optionalEncoding?:any):string|Uint8Array|null {
   return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
 }
 
+browserTz():string|null
+browserTz(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+browserTz(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 14);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
 static startFeedbackSubmitRequest(builder:flatbuffers.Builder) {
-  builder.startObject(5);
+  builder.startObject(6);
 }
 
 static addBody(builder:flatbuffers.Builder, bodyOffset:flatbuffers.Offset) {
@@ -99,18 +106,23 @@ static addVersion(builder:flatbuffers.Builder, versionOffset:flatbuffers.Offset)
   builder.addFieldOffset(4, versionOffset, 0);
 }
 
+static addBrowserTz(builder:flatbuffers.Builder, browserTzOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(5, browserTzOffset, 0);
+}
+
 static endFeedbackSubmitRequest(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;
 }
 
-static createFeedbackSubmitRequest(builder:flatbuffers.Builder, bodyOffset:flatbuffers.Offset, attachmentOffset:flatbuffers.Offset, attachmentNameOffset:flatbuffers.Offset, channelOffset:flatbuffers.Offset, versionOffset:flatbuffers.Offset):flatbuffers.Offset {
+static createFeedbackSubmitRequest(builder:flatbuffers.Builder, bodyOffset:flatbuffers.Offset, attachmentOffset:flatbuffers.Offset, attachmentNameOffset:flatbuffers.Offset, channelOffset:flatbuffers.Offset, versionOffset:flatbuffers.Offset, browserTzOffset:flatbuffers.Offset):flatbuffers.Offset {
   FeedbackSubmitRequest.startFeedbackSubmitRequest(builder);
   FeedbackSubmitRequest.addBody(builder, bodyOffset);
   FeedbackSubmitRequest.addAttachment(builder, attachmentOffset);
   FeedbackSubmitRequest.addAttachmentName(builder, attachmentNameOffset);
   FeedbackSubmitRequest.addChannel(builder, channelOffset);
   FeedbackSubmitRequest.addVersion(builder, versionOffset);
+  FeedbackSubmitRequest.addBrowserTz(builder, browserTzOffset);
   return FeedbackSubmitRequest.endFeedbackSubmitRequest(builder);
 }
 }