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.