feat(binding): Hytale SDK glue

The only module that imports com.hypixel.*. Provides World.asExecutor,
EntityHandle adapters for Ref/PlayerRef/Player, scope helpers
(playerScope, worldScope, pluginScope), and installAsync() which wires
PlayerDisconnectEvent to PlayerScopes.cancel.

binding/README.md

@@ -0,0 +1,48 @@
+# `:binding`
+
+The Hytale-specific glue. This is the only module that imports anything from
+`com.hypixel.hytale.*` — everything else in the project is plain Kotlin you
+can compile without the SDK on the classpath.
+
+## What's in here
+
+```kotlin
+World.asExecutor(): WorldExecutor
+Ref<EntityStore>.toEntityHandle(world: World): EntityHandle
+PlayerRef.toEntityHandle(): EntityHandle
+Player.handle(): EntityHandle
+
+JavaPlugin.installAsync()    // wires PlayerDisconnectEvent → PlayerScopes.cancel
+
+playerScope(player): CoroutineScope
+worldScope(world):  CoroutineScope
+pluginScope(plugin): CoroutineScope
+```
+
+Each is a thin delegating wrapper. The interesting code lives in `:core` and
+`:ecs`.
+
+## No unit tests
+
+`World` and `WorldConfig` break MockK's bytecode retransformer on JDK 25
+(`InternalError: class redefinition failed`). Adding `mockk-agent` plus a JVM
+arg flag would let us mock them, but they'd be testing five lines of method
+delegation. Not worth the maintenance.
+
+The actual behaviour — dispatcher confinement, scope cancellation, the DSL —
+is covered by the `:core` and `:ecs` unit tests, which run in milliseconds
+against in-memory stubs.
+
+If you want to verify the binding against a live server, build the shaded
+JAR (`./gradlew :dist:shadowJar`), drop it in `mods/`, and call
+`installAsync()` from a plugin's `start()`. If `playerScope(player).launch { modify<T>(...) { ... } }`
+runs without throwing `Assert not in thread!`, the binding works.
+
+## Known SDK gotchas
+
+- **No `WorldUnloadEvent`.** Until it ships, call `WorldScopes.cancel(uuid)`
+  yourself when you unload a world.
+- **Race on world death.** If a world dies between an `isAlive()` check and
+  the actual `execute()` call, the task is silently dropped by Hytale's task
+  queue and the awaiting coroutine never completes. Wrap long world-bound
+  work in `withTimeout(...)` if it matters.