Update dependencies and migrate to Gradle 9 / Dokka v2

Dependency bumps: Kotlin 2.3.20->2.3.21, Coroutines 1.10.2->1.11.0,
Ktor 3.4.2->3.5.1, KSP 2.3.6->2.3.9, MicroUtils 0.29.2->0.30.0,
Dokka 2.0.0->2.2.0, Versions plugin 0.53.0->0.54.0, NMCP 1.4.4->1.6.0.

Gradle wrapper 8.13->9.6.1 with build-script fixes for Gradle 9:
Project.exec() -> providers.exec(), tasks.whenTaskAdded -> tasks.configureEach.

Dokka migrated to the Dokka Gradle Plugin v2. The docs module is now
included as the KDocs aggregator (dokka {} DSL with sourceRoots, new URI,
ProcessIsolation heap for the generator worker), excluded from binary
compatibility validation, and the kdocs workflow runs :docs:dokkaGenerate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

settings.gradle

@@ -1,11 +1,4 @@
 pluginManagement {
-    resolutionStrategy {
-        eachPlugin {
-            if (requested.id.id == "org.jetbrains.dokka") {
-                useModule("org.jetbrains.dokka:dokka-gradle-plugin:${requested.version}")
-            }
-        }
-    }
     repositories {
         gradlePluginPortal()
     }
@@ -19,3 +12,4 @@ include ":tgbotapi.behaviour_builder"
 include ":tgbotapi.behaviour_builder.fsm"
 include ":tgbotapi"
 include ":tgbotapi.webapps"
+include ":docs"