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/server/handlers_feedback.go

@@ -19,6 +19,9 @@ type feedbackSubmitRequest struct {
 	// Version is the client's app version (pkg/version / the SPA build), snapshotted so the
 	// operator sees which build a report came from.
 	Version string `json:"version"`
+	// BrowserTZ is the client's detected UTC offset ("±HH:MM") at submit, so the operator can
+	// see the filed time in the sender's local zone even before they save a profile.
+	BrowserTZ string `json:"browser_tz"`
 }
 
 // feedbackReplyDTO is the operator's reply shown back to the player.
@@ -64,7 +67,7 @@ func (s *Server) handleFeedbackSubmit(c *gin.Context) {
 		}
 		attachment = data
 	}
-	if err := s.feedback.Submit(c.Request.Context(), uid, req.Body, attachment, req.AttachmentName, req.Channel, req.Version, clientIP(c)); err != nil {
+	if err := s.feedback.Submit(c.Request.Context(), uid, req.Body, attachment, req.AttachmentName, req.Channel, req.Version, req.BrowserTZ, clientIP(c)); err != nil {
 		s.abortErr(c, err)
 		return
 	}