Honor bound platform

- Route shared runtime hooks through the active Iris platform instead of classpath presence.
- Keep Bukkit-specific mantle and Matter behavior behind explicit platform capabilities.
- Cover hybrid classpaths and bound hook precedence with regression tests.

spi/src/main/java/art/arcane/iris/spi/IrisPlatform.java

@@ -66,6 +66,14 @@ public interface IrisPlatform {
      */
     PlatformBiomeWriter biomeWriter();
 
+    default Class<?> classifyMantleValue(Object value) {
+        return value.getClass();
+    }
+
+    default boolean supportsMatterWorldIo() {
+        return false;
+    }
+
     /**
      * Root folder Iris owns for packs, settings and generated data. Created if missing. Never null.
      */