refactor: redesign plugin system and enhance message handling

- Move plugin and tool-related classes to a dedicated `Plugin-API` module.
- Introduce a new plugin lifecycle (`onInit`, `onEnable`, `onDisable`) and a more robust `Tool` API.
- Refactor `Core` to use `PrintAdvanceMessageHandler` for improved handling of assistant messages, tool responses, and errors.
- Rename `PluginLoader` to `Loader` and migrate it to `me.zacharias.chat.plugin.loader`.
- Update build configurations and Java toolchains across modules.
- Clean up obsolete plugin annotations and interfaces in the `Core` module.

Core/build.gradle

@@ -2,15 +2,29 @@ plugins {
     id 'java-library'
 }
 
-group = 'me.zacharias'
-version = '1.3'
+group = 'me.zacharias.neurodock'
+version = '1.5'
 
 dependencies {
-
+    implementation project(":Plugin-API")
+    api "org.json:json:20250107"
 }
 
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(21)) // Set Java version
+        languageVersion.set(JavaLanguageVersion.of(javaVersion)) // Set Java version
+    }
+}
+
+// Tell shadow not to interfere with the main publication
+shadowJar {
+    archiveClassifier = 'all'  // keeps shadow as -all.jar, not the main artifact
+}
+
+configurations {
+    [apiElements, runtimeElements].each {
+        it.outgoing.artifacts.removeIf {
+            it.buildDependencies.getDependencies(null).contains(shadowJar)
+        }
     }
 }