feat(interface): add authoring macros and codecs

Add the wip-interface facade and proc-macro implementation for typed interface descriptors, DTO value codecs, validated dispatch, metadata extraction, and span-aware compile failures.

crates/wip-interface/tests/ui/tuple_dto.rs

@@ -0,0 +1,6 @@
+use wip_interface::WipType;
+
+#[derive(WipType)]
+struct TupleDto(String, String);
+
+fn main() {}