feat(account): seed the time zone from the client's detected offset at creation

A new account's time_zone defaulted to 'UTC' until the player saved a profile, so the
robot's sleep window and the turn-timeout away-window sweeper — both anchored to the
account zone via account.ResolveZone — ran on UTC for every fresh player, skewing
robot-game timing until a manual Settings save. Seed the zone at creation instead, from
the client's detected "±HH:MM" offset.

- Carry browser_tz on the three account-creating auth requests (TelegramLoginRequest,
  GuestLoginRequest, EmailRequestRequest — the email account is provisioned at the
  code-request step, not at login) through the fbs envelope (+ Go/TS codegen), the
  gateway transcode + backend client, and the backend auth handlers into
  ProvisionTelegram / ProvisionGuest / ProvisionEmail.
- create() now writes time_zone explicitly: the validated detected offset, or 'UTC'
  (equal to the column default) when absent or malformed — deterministic, never guessed.
  The column is already NOT NULL DEFAULT 'UTC', so no migration is needed and existing
  accounts keep 'UTC'. An existing account is never overwritten on re-login.
- A detected zero offset is stored as "+00:00" (the zone is known and equals UTC),
  distinct from the "UTC" default that means "unknown" — which the feedback console's
  three-zone Filed display already reflects.
- Guard the guest handler against an empty payload (the bootstrap historically carried
  none) so it degrades to no-seed rather than panicking in GetRootAs*.
- Tests: zone seeding across Telegram/guest/email plus the "+00:00"/malformed/empty
  cases and the not-overwrite rule; codec round-trip for the three auth encoders.
  ARCHITECTURE + FUNCTIONAL(+ru) updated.

pkg/fbs/scrabble.fbs

@@ -99,24 +99,33 @@ table MoveRecord {
 // --- auth (unauthenticated) ---
 
 // TelegramLoginRequest carries the platform launch data; the gateway validates
-// its HMAC before forwarding the extracted identity to the backend.
+// its HMAC before forwarding the extracted identity to the backend. browser_tz is
+// the client's detected UTC offset ("±HH:MM"), seeded into a brand-new account's
+// time zone so the robot's sleep window and the turn-timeout away window are
+// anchored to the player's real zone from first contact (first contact only).
 table TelegramLoginRequest {
   init_data:string;
+  browser_tz:string;
 }
 
 // GuestLoginRequest bootstraps an ephemeral guest session. locale is an optional
-// preferred-language hint.
+// preferred-language hint; browser_tz is the detected UTC offset seeded into the
+// guest account's time zone (see TelegramLoginRequest.browser_tz).
 table GuestLoginRequest {
   locale:string;
+  browser_tz:string;
 }
 
-// EmailRequestRequest asks the backend to send a login confirm-code to email.
+// EmailRequestRequest asks the backend to send a login confirm-code to email. It
+// also provisions the account on first contact, so browser_tz (the detected UTC
+// offset) is seeded into its time zone here, not at the later login step.
 table EmailRequestRequest {
   email:string;
+  browser_tz:string;
 }
 
-// EmailLoginRequest logs in (or provisions) the account owning email, verifying
-// the confirm-code.
+// EmailLoginRequest logs in to the account owning email (provisioned at the
+// request step), verifying the confirm-code.
 table EmailLoginRequest {
   email:string;
   code:string;

pkg/fbs/scrabblefb/EmailRequestRequest.go

@@ -49,12 +49,23 @@ func (rcv *EmailRequestRequest) Email() []byte {
 	return nil
 }
 
+func (rcv *EmailRequestRequest) BrowserTz() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
 func EmailRequestRequestStart(builder *flatbuffers.Builder) {
-	builder.StartObject(1)
+	builder.StartObject(2)
 }
 func EmailRequestRequestAddEmail(builder *flatbuffers.Builder, email flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(email), 0)
 }
+func EmailRequestRequestAddBrowserTz(builder *flatbuffers.Builder, browserTz flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(browserTz), 0)
+}
 func EmailRequestRequestEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }

pkg/fbs/scrabblefb/GuestLoginRequest.go

@@ -49,12 +49,23 @@ func (rcv *GuestLoginRequest) Locale() []byte {
 	return nil
 }
 
+func (rcv *GuestLoginRequest) BrowserTz() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
 func GuestLoginRequestStart(builder *flatbuffers.Builder) {
-	builder.StartObject(1)
+	builder.StartObject(2)
 }
 func GuestLoginRequestAddLocale(builder *flatbuffers.Builder, locale flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(locale), 0)
 }
+func GuestLoginRequestAddBrowserTz(builder *flatbuffers.Builder, browserTz flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(browserTz), 0)
+}
 func GuestLoginRequestEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }

pkg/fbs/scrabblefb/TelegramLoginRequest.go

@@ -49,12 +49,23 @@ func (rcv *TelegramLoginRequest) InitData() []byte {
 	return nil
 }
 
+func (rcv *TelegramLoginRequest) BrowserTz() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
 func TelegramLoginRequestStart(builder *flatbuffers.Builder) {
-	builder.StartObject(1)
+	builder.StartObject(2)
 }
 func TelegramLoginRequestAddInitData(builder *flatbuffers.Builder, initData flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(initData), 0)
 }
+func TelegramLoginRequestAddBrowserTz(builder *flatbuffers.Builder, browserTz flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(browserTz), 0)
+}
 func TelegramLoginRequestEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }