Fix damageable trigger brush weapon hits

[agustin-lowpoly]

Summary

• include health-bearing trigger brush models in singleplayer weapon target traces
• let projectile traces hit the same damageable trigger brushes as hitscan/melee/beam traces
• add focused coverage for E1M1-style trigger_multiple shoot targets and projectile damage

Validation

• node --test test/gameplay/weaponDamageableBrushTargets.test.mjs test/runtime/damageableBrushFlow.test.mjs
• node --test test/prepare/sceneVariants.test.mjs test/runtime/entities.test.mjs test/runtime/moversZeroTravelButton.test.mjs test/runtime/gameplayInputFlow.test.mjs test/runtime/damageableBrushFlow.test.mjs test/gameplay/playerWaterMove.test.mjs test/gameplay/weaponDamageableBrushTargets.test.mjs test/multiplayer/presence.test.mjs
• pnpm test
• pnpm build
• pnpm test:browser -- --family projectile --timeout-ms 90000
• browser probes confirmed E1M1 entity 138 responds to shotgun and nailgun projectile hits