refactor: split large modules and normalize rust layout

server-rs/crates/api-server/src/generated_image_assets.rs

@@ -0,0 +1,13 @@
+// 中文注释：C0 先落公共骨架，真实调用方迁移到 C1 后再移除未使用豁免。
+#![allow(dead_code, unused_imports)]
+
+pub mod adapter;
+pub mod helpers;
+
+pub(crate) use adapter::{GeneratedImageAssetAdapter, GeneratedImageAssetAdapterBoundary};
+pub(crate) use helpers::{
+    GeneratedImageAssetDataUrl, GeneratedImageAssetImageFormat, GeneratedImageAssetMetadataInput,
+    GeneratedImageAssetStoragePaths, build_generated_image_asset_metadata,
+    build_generated_image_asset_storage_paths, decode_generated_image_asset_data_url,
+    merge_generated_image_asset_metadata, normalize_generated_image_asset_mime,
+};