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/lib/codec.test.ts

@@ -76,20 +76,22 @@ describe('codec', () => {
   it('round-trips a feedback submit and decodes state + unread', () => {
     const att = new Uint8Array([1, 2, 3, 4]);
     const req = fb.FeedbackSubmitRequest.getRootAsFeedbackSubmitRequest(
-      new ByteBuffer(encodeFeedbackSubmit('please fix', att, 'shot.png', 'ios', 'v1.2.3')),
+      new ByteBuffer(encodeFeedbackSubmit('please fix', att, 'shot.png', 'ios', 'v1.2.3', '+03:00')),
     );
     expect(req.body()).toBe('please fix');
     expect(req.attachmentName()).toBe('shot.png');
     expect(req.channel()).toBe('ios');
     expect(req.version()).toBe('v1.2.3');
+    expect(req.browserTz()).toBe('+03:00');
     expect(Array.from(req.attachmentArray() ?? [])).toEqual([1, 2, 3, 4]);
 
     // No attachment: the vector is empty.
     const req2 = fb.FeedbackSubmitRequest.getRootAsFeedbackSubmitRequest(
-      new ByteBuffer(encodeFeedbackSubmit('hi', null, '', 'web', 'dev')),
+      new ByteBuffer(encodeFeedbackSubmit('hi', null, '', 'web', 'dev', '+00:00')),
     );
     expect(req2.body()).toBe('hi');
     expect(req2.version()).toBe('dev');
+    expect(req2.browserTz()).toBe('+00:00');
     expect(req2.attachmentLength()).toBe(0);
 
     // State carrying a reply.