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.

gateway/internal/backendclient/api_feedback.go

@@ -27,13 +27,14 @@ type FeedbackUnreadResp struct {
 
 // FeedbackSubmit posts a feedback message. The attachment bytes are base64-encoded
 // into the JSON body for the internal hop; clientIP rides X-Forwarded-For.
-func (c *Client) FeedbackSubmit(ctx context.Context, userID, body string, attachment []byte, attachmentName, channel, version, clientIP string) error {
+func (c *Client) FeedbackSubmit(ctx context.Context, userID, body string, attachment []byte, attachmentName, channel, version, browserTz, clientIP string) error {
 	payload := map[string]string{
 		"body":            body,
 		"attachment":      "",
 		"attachment_name": attachmentName,
 		"channel":         channel,
 		"version":         version,
+		"browser_tz":      browserTz,
 	}
 	if len(attachment) > 0 {
 		payload["attachment"] = base64.StdEncoding.EncodeToString(attachment)