feat(lookup): add Catalog::lookup_entries for listing a kind's vocabulary

[e54-bot]

Summary

Adds Catalog::lookup_entries(locale, kind) — a public call that returns one LookupMatch per catalog entry of a listable kind in catalog order, with no query, matching, or ranking. This supplies the owner side of Wright's listEntries operation (ADR-0031, wrightkit/wright#799): Wright pages over the result and assembles no signatures.

• Kind::Action, Kind::Value, Kind::Event → LookupMatch::Builtin, signature included.
• Kind::Enum → LookupMatch::EnumDomain per declared domain; enum members remain covered by lookup_within with no query.
• Undeclared locale → WorkshopError::Unsupported, as in lookup; non-listable kinds (Structural, Operator, Setting) → WorkshopError::Unsupported.
• The per-entry match construction is factored out of lookup's loops (builtin_match, enum_domain_match, shared check_locale), so listing and ranked lookup cannot diverge.
• Additive public API; no LookupMatch variants added or reordered; no catalog-generated items (ADR-0016).
• docs/lookup.md: new "Listing entries" section next to "Scoped lookup".

Fixes #506

Test plan

• listing_entries_keeps_catalog_order_for_each_builtin_kind: for Action, Value, and Event the listed ids equal entries_of(kind) ids in the same order, no duplicates.
• listing_entries_keeps_catalog_order_for_enum_domains: listed domains equal enum_domains() in the same order.
• listed_entries_are_the_matches_lookup_returns: every listed entry of each listable kind equals the lookup match of the same kind and id for a query of that id — in en-US (primary) and zh-CN. The comparison matches on kind and id because modifyGlobalVariable is declared under both Structural and Action, so a bare-id query can rank a different kind's Builtin first.
• listing_entries_rejects_undeclared_locales_and_unlistable_kinds: undeclared locale and non-listable kinds return WorkshopError::Unsupported.
• Gates: cargo fmt --all --check, cargo clippy --workspace --all-targets -- -D warnings, cargo test --workspace --all-targets, cargo run -p workshop-rs --bin workshop-catalog-gen -- check, cargo +1.85.0 clippy --workspace --all-targets -- -D warnings, cargo +1.85.0 test --workspace --all-targets, git diff --check — all pass locally.

[Teakowa]

LGTM