fix(tauri): add @reserved annotations to 3 unconnected commands

- classroom_chat_history: @reserved (no frontend consumer)
- orchestration_execute: @reserved (no frontend consumer)
- orchestration_validate: @reserved (no frontend consumer)

Update AUDIT_TRACKER: V11-P2-05 verified (89 connected / 18 @reserved)
DEAD-05 re-evaluated: 12 truly dead methods (not 39), documented in tracker

desktop/src-tauri/src/classroom_commands/chat.rs

@@ -114,7 +114,7 @@ pub async fn classroom_chat(
 }
 
 /// Retrieve chat history for a classroom
-// @connected
+// @reserved: no frontend consumer yet
 #[tauri::command]
 pub async fn classroom_chat_history(
     chat_store: State<'_, ChatStore>,