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/nested.txt

@@ -0,0 +1,25 @@
+interface "/::example" {
+  /// "type summary"
+  type Z = {
+    /// "field summary"
+    z?: unit,
+    a: [union {
+      /// "case summary"
+      z,
+      /// ""
+      a(unit),
+      nested(enum {
+        /// "enum summary"
+        z,
+        a,
+      }),
+    }],
+  };
+  operation z(
+    z: unit,
+    a?: unit,
+  ) -> unit;
+  operation a()
+  /// "no params result"
+  -> unit;
+}