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_admin_console.go

@@ -1198,17 +1198,15 @@ func fmtTime(t time.Time) string {
 	return t.UTC().Format("2006-01-02 15:04")
 }
 
-// fmtTimeIn formats a timestamp in the named IANA zone (falling back to UTC when the zone is
-// empty or unknown), or "" when zero — for showing a time in a user's local zone beside UTC.
+// fmtTimeIn formats a timestamp in the given zone — a "±HH:MM" offset or an IANA name, resolved
+// by account.ResolveZone (falling back to UTC when empty or unknown) — or "" when zero. Used to
+// show a time in a user's local zone beside UTC; the offset form is what the profile editor and
+// the feedback browser-tz snapshot store, so it must not go through time.LoadLocation alone.
 func fmtTimeIn(t time.Time, tz string) string {
 	if t.IsZero() {
 		return ""
 	}
-	loc, err := time.LoadLocation(tz)
-	if err != nil {
-		loc = time.UTC
-	}
-	return t.In(loc).Format("2006-01-02 15:04")
+	return t.In(account.ResolveZone(tz)).Format("2006-01-02 15:04")
 }
 
 // fmtTimePtr formats an optional timestamp for display, or "" when nil.

backend/internal/server/handlers_admin_feedback.go

@@ -77,10 +77,16 @@ func (s *Server) consoleFeedbackDetail(c *gin.Context) {
 		s.consoleError(c, err)
 		return
 	}
-	// Filed time: always UTC; plus the sender's local zone when it is set and not UTC.
-	localCreated := ""
+	// Filed time in three zones so the operator can tell what is certainly known from what is
+	// merely defaulted: always UTC; the client's offset detected at submit (when the build
+	// reported one); and the sender's saved profile zone (when set beyond the UTC default). An
+	// empty rendered time makes the template show "N/A" for that line.
+	browserCreated, userCreated := "", ""
+	if m.BrowserTZ != "" {
+		browserCreated = fmtTimeIn(m.CreatedAt, m.BrowserTZ)
+	}
 	if m.TimeZone != "" && m.TimeZone != "UTC" {
-		localCreated = fmtTimeIn(m.CreatedAt, m.TimeZone)
+		userCreated = fmtTimeIn(m.CreatedAt, m.TimeZone)
 	}
 	view := adminconsole.FeedbackDetailView{
 		ID: m.ID.String(), AccountID: m.AccountID.String(), SenderName: m.SenderName,
@@ -89,7 +95,9 @@ func (s *Server) consoleFeedbackDetail(c *gin.Context) {
 		HasAttachment: m.HasAttachment, AttachmentName: m.AttachmentName, IsImage: feedback.IsImage(m.AttachmentName),
 		Read: m.Read, Archived: m.Archived, Replied: m.Replied, ReplyBody: m.ReplyBody,
 		RepliedAt: fmtTime(m.RepliedAt), CreatedAt: fmtTime(m.CreatedAt),
-		Version: m.Version, CreatedAtLocal: localCreated, TimeZone: m.TimeZone,
+		Version:          m.Version,
+		CreatedAtBrowser: browserCreated, BrowserTZ: m.BrowserTZ,
+		CreatedAtUser: userCreated, UserTZ: m.TimeZone,
 	}
 	if banned, err := s.accounts.HasRole(ctx, m.AccountID, account.RoleFeedbackBanned); err == nil {
 		view.Banned = banned

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
 	}