fix(game): release a banished race's assets during turn generation

TurnWipeExtinctRaces iterated only non-extinct races, so an
administratively banished race (flagged extinct, TTL untouched) was never
wiped: its planets stayed owned and its ships lingered, while the race
itself could no longer act. The loop now covers every race and wipes when
either an active race's TTL has run out (idle / quit) or an extinct race
still holds assets (banish). The asset check makes repeated passes
idempotent.

wipeRace already matched the rules for exclusion (ships removed, planets
uninhabited, industry and capital cleared, material retained), so the
behaviour is just documented in game/README.md.

Tests: banish releases planets and ships on the next turn (and is
idempotent); idle-timeout wipe still fires under the new iterator.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

game/README.md

@@ -102,9 +102,13 @@ remove-and-banish flow.
   non-empty and must match an existing race in the engine's roster.
 - Successful response: `204 No Content` with an empty body.
 - Error responses follow the same `400` / `500` envelope shape as the
-  other admin endpoints. The engine-side mechanics of `banish` (what
-  exactly happens to the race's planets, fleets, and pending orders) are
-  owned by the engine maintainers.
+  other admin endpoints. `banish` only flags the race extinct, so it can
+  no longer submit or have orders applied; its assets are released at the
+  start of the next turn generation (`TurnWipeExtinctRaces`), the same way
+  an idle/quit timeout is handled but without the wait — ship groups and
+  fleets are removed, its planets become uninhabited (the working industry
+  and the capital stockpile are cleared, raw material is retained), and
+  votes cast for it are reset.
 
 ### `GET /healthz`