Fix SpacetimeDB wasm dependency boundary

server-rs/crates/shared-contracts/Cargo.toml

@@ -4,7 +4,12 @@ edition.workspace = true
 version.workspace = true
 license.workspace = true
 
+[features]
+# 默认给 api-server 等原生后端保留资产上传契约；SpacetimeDB WASM 路径通过 workspace 依赖关闭默认 feature。
+default = ["oss-contracts"]
+oss-contracts = ["dep:platform-oss"]
+
 [dependencies]
-platform-oss = { workspace = true }
+platform-oss = { workspace = true, optional = true }
 serde = { workspace = true }
 serde_json = { workspace = true }