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/issue-read.txt

@@ -0,0 +1,22 @@
+/// "Issueの内容と関連項目を読む。"
+interface "/::issue.read" {
+  type Relation = enum {
+    parent,
+    sibling,
+    related,
+  };
+  type RelatedItems = {
+    /// "同じWorldspace内の関連項目。"
+    items: [entry],
+    next_cursor?: string,
+  };
+  /// "本文を取得する。"
+  operation read_body() -> {
+    body: string,
+  };
+  /// "関係を指定して関連項目を取得する。"
+  operation get_related_items(
+    relation: Relation,
+    limit?: integer,
+  ) -> RelatedItems;
+}