feat: add Elytra mode (basic S-level)

- elytra/section/: ElytraSection (5 knots + cubic spline via commons-math3),
  ElytraKnotDirector (dx~N(75,15), dy bias, dz~N(0,35)), ElytraPointType
  (CIRCLE Bresenham / FLAT), ClientBlockChanger (client-side sendBlockChanges,
  forward-limit min(vd,8))
- elytra/generator/ElytraGenerator extends ParkourGenerator: own tick() (score by
  velocity.x while gliding, section lifecycle, fall detection, sustained boost in
  ascending sections), reset, spawn with elytra
- elytra/mode/ElytraMode: registered in Modes/PluginBootstrap, locale items ru/en
- build.gradle: commons-math3 3.6.1 + relocate
- checkstyle 0/0, PMD 0, build green (tests + shadowJar)

src/main/java/dev/loki/loparkour/mode/base/Modes.java

@@ -1,6 +1,7 @@
 package dev.loki.loparkour.mode.base;
 
 import dev.loki.loparkour.api.core.Registry;
+import dev.loki.loparkour.elytra.mode.ElytraMode;
 import dev.loki.loparkour.mode.impl.barrier.InvisibleBarrierMode;
 import dev.loki.loparkour.mode.impl.multi.CoopMode;
 import dev.loki.loparkour.mode.impl.multi.RaceMode;
@@ -21,6 +22,7 @@ public final class Modes {
     public static RaceMode RACE;
     public static CoopMode COOP;
     public static GravityShiftMode GRAVITY_SHIFT;
+    public static ElytraMode ELYTRA;
 
     public static void init() {
         DEFAULT = (DefaultMode) Registry.getMode("default");
@@ -30,5 +32,6 @@ public final class Modes {
         RACE = (RaceMode) Registry.getMode("race");
         COOP = (CoopMode) Registry.getMode("coop");
         GRAVITY_SHIFT = (GravityShiftMode) Registry.getMode("gravity-shift");
+        ELYTRA = (ElytraMode) Registry.getMode("elytra");
     }
 }