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.

docs/ARCHITECTURE.md

@@ -649,7 +649,11 @@ in either direction (the enqueue excludes the caller's `BlockedWith` set);
   separators (no leading/trailing/adjacent separators, ≤ 32 runes); the timezone is a
   fixed `±HH:MM` **UTC offset** (or a legacy IANA name) resolved by `account.ResolveZone`
   for the sweeper and the robot's sleep (a fixed offset trades DST for a simple
-  picker); the away window is at most **12 h** (midnight-wrap aware). Linked platform
+  picker), and is **seeded at account creation** from the client's detected offset — sent
+  on the Telegram / guest / email first-contact request — so the robot's sleep and the
+  away-window sweeper are anchored to the player's real zone from the first game rather
+  than the `UTC` default (an undetected or malformed offset keeps the default); the away
+  window is at most **12 h** (midnight-wrap aware). Linked platform
   accounts and merge are covered in §4.
 
 ## 9. Persistence