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/FUNCTIONAL.md

@@ -241,7 +241,8 @@ also clears the moment its recipient **takes their move**.
 Edit the display name (letters joined by a single space / "." / "_" separator, with an
 optional trailing "." or a trailing run of up to five digits, up to 32 characters and at most
 5 special characters — the "." / "_" punctuation, spaces and digits aside), the timezone
-(chosen as a UTC offset), the
+(chosen as a UTC offset, and pre-filled from your device's detected offset when the account
+is first created — so robot games are timed correctly before you ever open this form), the
 daily away window (on a 10-minute grid, at most 12 hours, wrapping midnight) and the
 block toggles. The profile form is edited inline (no separate edit mode). Linking
 an email or Telegram and merging accounts are covered under "Accounts, linking &