feat(ai): 知识库 V2 Handler + 路由注册 + State 初始化

5 个端点：GET/POST /ai/knowledge-bases, GET/PUT/DELETE /ai/knowledge-bases/{id}
AiState 新增 knowledge_v2 字段，main.rs 初始化。

crates/erp-server/src/main.rs

@@ -616,6 +616,9 @@ async fn main() -> anyhow::Result<()> {
                     erp_ai::service::embedding::EmbeddingService::from_settings(&db).await,
                 ),
             )),
+            knowledge_v2: std::sync::Arc::new(
+                erp_ai::service::knowledge_v2::KnowledgeV2Service::new(db.clone()),
+            ),
             chat_session: std::sync::Arc::new(
                 erp_ai::service::chat_session::ChatSessionService::new(db.clone()),
             ),