Initial project setup for MoreStrongholds mod

Add core mod files, build configuration, mixin for stronghold placement, and data resources to enable extended stronghold generation in Minecraft. Includes Gradle setup, MIT license, mod metadata, and structure definitions.

settings.gradle

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