refactor: clean GSD comments and translate remaining Java sources to English

- Reduce javadocs to one-liners across config/region/physics/tick/viz/plugin root

- Translate residual French comments; no behavioural change

- Tests adjusted where assertions referenced French strings

src/test/java/com/mythlane/gravityflip/physics/FallDamageGuardTest.java

@@ -10,10 +10,7 @@ import java.util.UUID;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-/**
- * Pure-data tests for {@link FallDamageGuard} — no Hytale runtime dependency.
- * Covers entry / in-region / exit / grace-window / re-entry / FallDamage=true override.
- */
+/** Pure-data tests for {@link FallDamageGuard} — entry, in-region, exit, grace-window, re-entry. */
 class FallDamageGuardTest {
 
     @Test
@@ -69,8 +66,7 @@ class FallDamageGuardTest {
         GravityFlipRegion region = region(false, 2500);
         guard.markInRegion(uuid, region);
         guard.markExit(uuid, region, 1000L);
-        guard.markInRegion(uuid, region);  // re-enter
-        // In-region again with FallDamage=false → immediate suppression, grace reset.
+        guard.markInRegion(uuid, region);
         assertTrue(guard.shouldSuppressFallDamage(uuid, 1500L));
     }
 
@@ -82,7 +78,6 @@ class FallDamageGuardTest {
         GravityFlipRegion allowed = region(true, 2500);
         guard.markInRegion(uuid, suppressed);
         guard.markExit(uuid, suppressed, 1000L);
-        // New region has FallDamage=true → override immediately.
         guard.markInRegion(uuid, allowed);
         assertFalse(guard.shouldSuppressFallDamage(uuid, 1500L));
     }