chore: 编译器警告清理 — 22 条全部消除，workspace 零警告

erp-ai(8): 移除未用 import + serde 结构体 #[allow(dead_code)]
erp-plugin(5): 移除未用 import + FromQueryResult 结构体允许
erp-health(8): 移除未用 import/变量 + FromQueryResult 字段允许
erp-server(1): AnalyticsEvent.timestamp 允许（未来分析集成）

crates/erp-ai/src/handler/suggestion_handler.rs

@@ -100,9 +100,9 @@ where
 {
     require_permission(&ctx, "ai.suggestion.list")?;
 
-    use crate::entity::ai_suggestion;
-    use sea_orm::{ColumnTrait, EntityTrait, QueryFilter};
+    use sea_orm::EntityTrait;
 
+    use crate::entity::ai_suggestion;
     let suggestion = ai_suggestion::Entity::find_by_id(id)
         .one(&state.db)
         .await