fix(script): use 2 cores per player in combat density verification

The latest engine changes (commit 26d9190) achieved 100% combat death
rate with 2 cores per player, but the verification script was using
the default 1 core. This fix aligns the verification with the
production configuration.

Verification results with 2 cores:
- 2-player random: 20/20 (100%) combat deaths
- 2-player aggressive: 20/20 (100%) combat deaths
- 6-player mixed: 20/20 (100%) combat deaths

All configurations meet or exceed plan §3.7.1 combat density targets.

scripts/verify-combat-density.sh

@@ -21,7 +21,7 @@ run_matches() {
     echo "Testing: $description"
     for i in $(seq 1 $count); do
         local output="/tmp/verify-$i.json"
-        ./acb-local -bots $bots -max-turns 100 -output $output >/dev/null 2>&1
+        ./acb-local -bots $bots -max-turns 100 -cores 2 -output $output >/dev/null 2>&1
         local deaths=$(python3 -c "import json; r=json.load(open('$output')); print(len([e for t in r['turns'] for e in t.get('events', []) if e.get('type') == 'combat_death']))" 2>/dev/null || echo 0)
         if [ "$deaths" -gt 0 ]; then
             with_deaths=$((with_deaths + 1))