refactor: drop unused VFX scaffolding, single-line English doc, reduce debug logs

- Remove unused chain/ParticleTrail and chain/VolumeCurve (dead since the EntityEffect
  pivot replaced the per-particle emit path) plus their test suites.
- Drop Vec3.lerp (only consumer was ParticleTrail).
- Strip step-by-step "[N/9]" debug logs from the orchestrator and per-entity logs
  from HytaleEntitySource / HytalePlayerRayCaster / ChainDamageApplier; keep one
  summary log per click and warnings on failure.
- Extract resolveChain and tryEmitVfx helpers in ChainLightningSceptreInteraction
  so firstRun reads top-down (cooldown gate -> resolve -> damage -> vfx -> deduct).
- Translate every Java doc/comment to single-line English.

Tests: 30/30 green (29 baseline kept + 1 chain damage adapter test).
Build: ./gradlew shadowJar clean.

src/main/java/com/mythlane/chainlightning/chain/ChainEntity.java

@@ -1,9 +1,6 @@
 package com.mythlane.chainlightning.chain;
 
-/**
- * Contrat minimal d'une cible de chaîne. Stable, mockable, sans dépendance Hytale.
- * Phase 3 adaptera l'entité Hytale vers ChainEntity à la frontière.
- */
+/** Minimal chain target contract — stable, mockable, no Hytale dependency. */
 public interface ChainEntity {
     String id();
     Vec3 position();