feat: add standalone WIP Text View signatures

Render one Object or paired Interface entity without path/context, lookups or wire-schema changes. Preserve declarations, summaries, optional/unit and empty distinctions; validate protocol semantics and bounded input before rendering. Add five spec/nested goldens and 13 external API tests plus a standalone doctest.

Validation: cargo fmt --all -- --check; cargo check --workspace --all-targets; cargo test --workspace --all-targets; cargo test --workspace --doc; nix develop -c bash (cargo clippy --workspace --all-targets -- -D warnings, RUSTDOCFLAGS='-D warnings' cargo doc --workspace --no-deps, cargo run --package wip-public-api-example); git diff --check. All passed. Default shell lacks clippy; declared Nix dev shell supplied it.

crates/wip-text-view/tests/golden/identifiers.txt

@@ -0,0 +1,8 @@
+interface "/::example" {
+  type `string` = {
+    `表示名`: string,
+  };
+  operation `find-item`(
+    `search term`: string,
+  ) -> `string`;
+}