Redesign plugins UI and demo raw + high-level hooks

- Match exteraGram-style card layout with master toggle and plugin actions
- Add usage manifest field, pin/delete/removePlugin engine APIs
- Hello World plugin hooks Logger.d (raw) and send pipeline (high-level)
- Bundle updated hello_world.fcplugin; stop debug auto-enable

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

plugins/sdk/src/commonMain/kotlin/ru/fromchat/plugins/PluginTypes.kt

@@ -66,6 +66,7 @@ data class PluginManifest(
     val description: String = "",
     val author: String = "",
     val version: String = "1.0.0",
+    val usage: String = "",
     val appVersion: String = "",
     val sdkVersion: String = "",
     val entryClass: String,