Stage 17 #5: hide finished games from your own lobby list

A player can remove a finished game from their own 'my games' list. The action is
per-account, finished-only and irreversible (the game stays for the other players;
there is no un-hide).

- backend: migration 00012 game_hidden(account_id, game_id); store HideGame +
  hiddenGameIDs + ListGamesForAccount filtering; service HideGame (seat + finished
  checks, reusing ErrNotAPlayer / ErrGameActive); POST /api/v1/user/games/:id/hide.
- gateway: game.hide edge op (reuses GameActionRequest -> Ack) + backendclient.HideGame.
- ui: finished rows reveal a delete via swipe-left (touch) or a kebab tap (desktop),
  active rows get an inert chevron for icon alignment; optimistic removal + lobby-cache
  sync; mock + transport + client wiring; lobby.hideGame label (en/ru).
- tests: integration (active->ErrGameActive, outsider->ErrNotAPlayer, per-account,
  idempotent), gateway transcode round-trip, mock e2e (kebab -> delete); hardened a
  pre-existing chat-screen .back transition flake surfaced by the new test's timing.
- docs: ARCHITECTURE persistence list, FUNCTIONAL (+ _ru) lobby story, PLAN tracker.

docs/ARCHITECTURE.md

@@ -419,6 +419,10 @@ English game the Latin pool.
   (pending confirm-codes) and `game_invitations` / `game_invitation_invitees`
   (friend-game invitations). Stage 8's migration `00006` widened the `friendships`
   status to admit `declined` and added `friend_codes` (one-time add-a-friend codes).
+  Stage 17 added `game_drafts` (a player's in-progress rack order + board composition per
+  game) and `game_hidden` (`(account_id, game_id)` rows that drop a finished game from one
+  account's own lobby list, leaving it visible to the other players — finished-only and
+  irreversible by design, so there is no un-hide).
   The matchmaking pool is **in-memory** and persists nothing.
 - **Active games are event-sourced.** A game is a `games` row (pinned
   `variant`/`dict_version`, bag `seed`, the per-game settings, and a denormalised