Add Kotlin plugin system (SDK, host, hooks, settings UI)

Implement exteraGram-style plugin architecture for Android and desktop:
- plugins/sdk: BasePlugin API, hook types, settings DSL
- plugins/host: PluginEngine, typed send hooks, FeatureGate, HookRegistry
- JVM ByteBuddy and Android Pine hook backends
- DevServer on port 42690 (JVM)
- Plugins settings screens and PluginUiHost bulletin overlay
- hello_world sample plugin packaged as .fcplugin
- ProGuard keepnames for ru.fromchat.** with shrinking enabled

Co-authored-by: denis0001-dev <denis0001.dev@ya.ru>

settings.gradle.kts

@@ -42,5 +42,13 @@ dependencyResolutionManagement {
     }
 }
 
-include(":app:shared", ":utils:shared", ":app:android", ":app:desktop")
+include(
+    ":app:shared",
+    ":utils:shared",
+    ":app:android",
+    ":app:desktop",
+    ":plugins:sdk",
+    ":plugins:host",
+    ":plugins:sample-hello",
+)