multiview 空白视图按未提供处理

to_sdk_params 新增 optional_view，将仅含空白的 left、back、right 归一化为未提供

空白视图不再以 Some(FileInput) 形式提交，与提交前“至少两个视图”的校验保持一致

server-rs/crates/platform-tripo/src/multiview_to_model/client.rs

@@ -79,6 +79,13 @@ impl TripoProviderClient {
         Ok(TripoTaskHandle { task_id })
     }
 }
+/// 与提交前校验保持一致：空白视图按未提供处理。
+fn optional_view(value: &Option<String>) -> Option<FileInput> {
+    value
+        .as_deref()
+        .filter(|value| !value.trim().is_empty())
+        .map(FileInput::from)
+}
 
 fn to_sdk_params(request: &Model3dMultiviewToModelRequest) -> MultiviewToModelParams {
     let mut params = match &request.inputs {
@@ -89,9 +96,9 @@ fn to_sdk_params(request: &Model3dMultiviewToModelRequest) -> MultiviewToModelPa
             right,
         } => MultiviewToModelParams::from_views([
             Some(FileInput::from(front.as_str())),
-            left.as_deref().map(FileInput::from),
-            back.as_deref().map(FileInput::from),
-            right.as_deref().map(FileInput::from),
+            optional_view(left),
+            optional_view(back),
+            optional_view(right),
         ]),
         Model3dMultiviewInputs::TaskId { task_id } => {
             MultiviewToModelParams::from_task_id(task_id.clone())