fix(db): add LIMITs to unbounded queries to prevent OOM

Added LIMIT clauses to 4 unbounded queries that were causing
acb-index-builder to crash with OOMKill after copying web assets:

- fetchPredictorStats: LIMIT 100 (was loading all predictor stats)
- fetchMaps: LIMIT 500 (was loading all maps)
- fetchSeasonSnapshots: LIMIT 1000 (was loading all season snapshots)
- fetchSeasons: LIMIT 100 (was loading all seasons)

These queries had ORDER BY but no LIMIT, causing them to load
massive datasets into memory on each build cycle, leading to
container OOM after the web asset copy phase.

Fixes bead bf-2ws

cmd/acb-index-builder/db.go

@@ -568,6 +568,7 @@ func fetchSeasons(ctx context.Context, db *sql.DB) ([]SeasonData, error) {
 		FROM seasons s
 		LEFT JOIN bots b ON s.champion_id = b.bot_id
 		ORDER BY s.starts_at DESC
+		LIMIT 100
 	`
 
 	rows, err := db.QueryContext(ctx, query)
@@ -644,6 +645,7 @@ func fetchSeasonSnapshots(ctx context.Context, db *sql.DB, seasonID int64) ([]Se
 		JOIN bots b ON ss.bot_id = b.bot_id
 		WHERE ss.season_id = $1
 		ORDER BY ss.rank
+		LIMIT 1000
 	`, seasonID)
 	if err != nil {
 		return nil, err
@@ -755,6 +757,7 @@ func fetchPredictorStats(ctx context.Context, db *sql.DB) ([]PredictorStats, err
 		SELECT predictor_id, correct, incorrect, streak, best_streak
 		FROM predictor_stats
 		ORDER BY (correct::float / NULLIF(correct + incorrect, 0)) DESC NULLS LAST
+		LIMIT 100
 	`
 
 	rows, err := db.QueryContext(ctx, query)
@@ -788,6 +791,7 @@ func fetchMaps(ctx context.Context, db *sql.DB) ([]MapData, error) {
 		) v ON m.map_id = v.map_id
 		WHERE m.status IN ('active', 'probation', 'classic')
 		ORDER BY m.engagement DESC
+		LIMIT 500
 	`
 
 	rows, err := db.QueryContext(ctx, query)