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.

PLAN.md

@@ -1415,9 +1415,18 @@ provided cert) at the contour caddy; prod VPN; rollback.
       and `--tg-content-top`), with a small padding bump so the native controls aren't flush.
     - **Tests backfilled** for the merged round-6 work: e2e for the in-game "✓ in friends" item
       and a board→board tile relocation; codec units for `last_activity_unix` + `OutgoingRequestList`.
+    - **Hide finished games (#5, shipped):** a player can remove a finished game from their own
+      *my games* list — **per-account, finished-only and irreversible** (the game stays for the
+      other players; there is no un-hide). On a finished row a **swipe-left** (touch) or a tap on
+      its **kebab ⋮** (the desktop affordance) reveals a **❌** that hides it; active rows carry an
+      inert **›** chevron purely to keep the right-edge icons aligned. New table
+      `game_hidden(account_id, game_id)` + migration `00012`; `ListGamesForAccount` filters the
+      hidden set; `POST /api/v1/user/games/:id/hide` behind the `game.hide` edge op (reusing
+      `GameActionRequest` → an `Ack`); the lobby drops the card optimistically and keeps the cache
+      in sync. Covered by an integration test (active→`ErrGameActive`, outsider→`ErrNotAPlayer`,
+      per-account visibility, idempotent), a gateway transcode test, and a mock e2e (kebab → ❌).
     - **Deferred to the next PR (agreed):** #4 enrich the out-of-app "your turn" / game-end push
-      with the opponent's name, last word and score; #5 let a player hide finished games from
-      their lobby (swipe + a desktop affordance).
+      with the opponent's name, last word and score.
 
 ## Deferred TODOs (cross-stage)