feat(link): auto-merge a guest initiator into its durable account (seamless sign-in)

When a guest links an identity (email/TG/VK) that already belongs to a durable account,
the guest-primary rule already made the durable account the survivor and switched the
session — but the client still showed an irreversible 'merge two accounts?' confirmation,
which is nonsense from the user's side (they are simply signing into their account). The
confirm step now merges inline for a GUEST initiator and returns the completed merge (the
switched token); a durable initiator still gets the explicit confirmation (consolidating
two real accounts is consequential). The active-game guard still refuses, surfaced as the
clear error.merge_active_game_conflict message rather than swallowed.

Also fixes the merged-away device-local games: their human/host seat was recorded under
the retired account id, so after the switch the lobby and game header could not identify
'me' and showed every seat as an opponent (the game still played — turn logic is
seat-index based). applyLinkResult now re-points local game seats from the retired id to
the survivor (repointLocalGameSeats).

Docs: FUNCTIONAL.md (+_ru).

docs/FUNCTIONAL.md

@@ -117,12 +117,15 @@ First platform contact auto-provisions a durable account. From the profile a pla
 links an email (via a confirm code) or their Telegram (via the web sign-in); a guest
 who links their first identity becomes a durable account. The "already taken" status
 of an identity is never revealed before the code/sign-in is verified. If the linked
-identity already belongs to another account, the player is shown an explicit,
-**irreversible** confirmation and the two accounts are merged into the one they are
-using (statistics summed, games and friends transferred, duplicates removed) — except
-when a guest links an identity that already has a durable account, where the durable
-account is kept and the guest's games move into it. A merge is blocked only while the
-two accounts share a game still in progress.
+identity already belongs to another account, the two accounts are merged into one
+(statistics summed, games and friends transferred, wallet folded, duplicates removed).
+A **durable** initiator is shown an explicit, **irreversible** confirmation first —
+consolidating two real accounts is consequential. A **guest** initiator is not: the
+durable account that owns the identity is kept, and the ephemeral guest — with its games,
+wallet and stats folded in — is retired **seamlessly**, so from the player's side it is
+simply signing into their account (the app switches to it with no prompt). A merge is
+blocked only while the two accounts share a game still in progress; a guest is then asked
+to finish that shared game before signing in.
 
 The profile lists the account's **sign-in methods**. On the web a player can add
 Telegram (a login-widget popup) or VK (VK ID web login — a redirect to VK's sign-in and