fix(server): populate games_v2 metadata on game start

update_game_started (started_at, num_players, num_rounds, player_ids)
was defined in event_store but had zero callers. 289/289 staging games
had those fields NULL — queries that joined on them returned garbage,
and the denormalized player_ids GIN index was dead weight.

log_game_start now calls create_game THEN update_game_started in one
async task. If create fails, update is skipped (row doesn't exist).
handlers.py passes num_rounds and player_ids through at call time.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/handlers.py

@@ -215,6 +215,8 @@ async def handle_start_game(data: dict, ctx: ConnectionContext, *, broadcast_gam
             ctx.current_room.game_log_id = game_logger.log_game_start(
                 room_code=ctx.current_room.code,
                 num_players=len(ctx.current_room.players),
+                num_rounds=num_rounds,
+                player_ids=[p.id for p in ctx.current_room.game.players],
                 options=options,
             )