updated to Paper 26.2, Java 25 and Gradle 9.6.1

- paper-api 26.2.build.129-stable (all modules), Java toolchain 25, shadow 9.6.1
- fixed NoSuchFieldError on join/quit/chat: Adventure 5 ClickEvent API
  (ClickEvent.suggestCommand / openUrl instead of ClickEvent.Action constants)
- fixed NBTComponent generics in AntiFormattedBook
- replaced javax.annotation with org.jetbrains.annotations (no longer provided by paper-api)
- local.gradle.example: Gradle 9 compatible (archiveFile, providers.exec)

The previous state is tagged as paper-1.21.10.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

build.gradle

@@ -1,6 +1,6 @@
 plugins {
     id 'java'
-    id 'com.gradleup.shadow' version "8.3.5"
+    id 'com.gradleup.shadow' version "9.6.1"
 }
 
 allprojects {
@@ -29,7 +29,7 @@ subprojects {
 
     java {
         toolchain {
-            languageVersion = JavaLanguageVersion.of(21)
+            languageVersion = JavaLanguageVersion.of(25)
         }
     }
 }