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/test/java/com/mythlane/chainlightning/chain/TestChainEntity.java

@@ -1,9 +1,6 @@
 package com.mythlane.chainlightning.chain;
 
-/**
- * Helper test record implémentant ChainEntity. Permet construction concise dans
- * les tests : entity("e1", 0, 0, 0) pour un vivant, dead("e2", 5, 0, 0) pour un mort.
- */
+/** Test-only ChainEntity record with concise factories for alive and dead entities. */
 record TestChainEntity(String id, Vec3 position, boolean isAlive) implements ChainEntity {
 
     static TestChainEntity entity(String id, double x, double y, double z) {