feat(variants): default a registered account to Erudit + Russian Scrabble

New Game opened on a single variant for everyone, which reads poorly on VK
where Russian Scrabble is the familiar game. A registered account now starts
with both Russian-alphabet games, so the picker offers a real choice with no
pre-selection.

A guest stays on Erudit alone and is invited to register for the rest: the
device-local guest has no profile at all, so the client-side fallback has to
keep matching the server. Registering promotes the set, but only while the
guest still carries the untouched guest default. Existing accounts are not
backfilled — the set they carry may be a deliberate choice.

The Telegram promo start-param becomes additive rather than a replacement,
with English Scrabble withheld from a Russian-speaking arrival; otherwise the
English campaign link would have taken Russian Scrabble away from every
account it onboarded.

apple/PLAN.md

@@ -501,7 +501,7 @@ emerge while implementing the vertical slice, step 3.)*
     toggle → **Start**.
   - *With friends:* rows **Invite a friend** / **Pass-and-play** → pushed sub-flows.
 - **Variant picker:** **emblem chips / segmented** (≤3 variants); **hidden entirely when a single variant
-  is enabled** (the common default — Erudite only).
+  is enabled** (a guest's default — Erudite only; a registered account starts with two).
 
 **Behaviour (per FUNCTIONAL, kept)**
 - **Quick game:** AI default (instant 🤖, no wait) / Random (auto-match 2p — drops you into the game to