Initial project setup for SilkSpawners mod

Add SilkSpawners mod source files, configuration, mixins, Gradle build scripts, and metadata for Fabric. Implements spawner drop logic, config loading/saving, and required interfaces/mixins for custom spawner behavior.

settings.gradle

@@ -0,0 +1,9 @@
+pluginManagement {
+    repositories {
+        maven {
+            name = 'Fabric'
+            url = 'https://maven.fabricmc.net/'
+        }
+        gradlePluginPortal()
+    }
+}