refactor(player): encapsulate game state behind PlayerSettings, clear VisibilityModifier and HiddenField

- ParkourUser/ParkourPlayer/GeneratorState public mutable fields -> private + short accessors
- per-player settings extracted to player/data/PlayerSettings (ParkourPlayer 188 -> 96 lines,
  PMD-counted methods 20 -> 9); this is what fixed the TooManyMethods violation that the
  encapsulation itself introduced — by decomposition, not by lowering the threshold
- disk storage reads and writes the same canonical 12-key map as the SQL JSON column;
  legacy key names normalized on read, @Expose dropped from domain classes
- 39 settings call sites rewritten across 7 files
- HiddenField backlog cleared (Config, ObstacleGenerator, GhostService, Leaderboard,
  PagedMenu, Reward, ParticleData, World)
- checkstyle ratchet: VisibilityModifier, HiddenField, EmptyLineSeparator and
  MissingDeprecated flipped to error once their counters hit zero; suppressions.xml empty
- javac -Xmaxwarns raised so NullAway/Error Prone counts are honest
  (baseline 165/289, now 164/265)

checkstyle 0 errors / 135 warnings, PMD 0 violations, tests 94/0 fail, ./gradlew check green.
TODO.md: items 30 and 107 updated, new items 167-170, ПРОГРЕСС-6/7 recorded.

src/main/java/dev/loki/loparkour/LoParkour.java

@@ -114,8 +114,8 @@ public final class LoParkour extends JavaPlugin {
                 ParkourUser.leave(user);
             }
 
-            if (Modes.DEFAULT != null && Modes.DEFAULT.getLeaderboard() != null) {
-                Modes.DEFAULT.getLeaderboard().write(false);
+            if (Modes.defaultMode() != null && Modes.defaultMode().getLeaderboard() != null) {
+                Modes.defaultMode().getLeaderboard().write(false);
             }
 
             Rewards.clear();