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/RayCaster.java

@@ -2,11 +2,7 @@ package com.mythlane.chainlightning.chain;
 
 import java.util.Optional;
 
-/**
- * Ray-cast retournant la première entité touchée le long du rayon, ou empty.
- * SAM permettant aux tests de fournir un résultat fixe et à Phase 3 de brancher
- * l'API Hytale réelle.
- */
+/** SAM that returns the first entity hit along a ray, or empty. */
 @FunctionalInterface
 public interface RayCaster {
     Optional<ChainEntity> firstHit(Vec3 origin, Vec3 direction, double maxBlocks);