figma-transformer: decode hyperlinks and reaction URL/navigation links

[chubes4]

Summary

Wires Figma hyperlinks and prototype navigation through the figma-transformer. Per coverage issue #328, the normalizer's normalizeReactionLink() / normalizeHyperlinkValue() and the emitter's <a class="figma-link"> wrapping already existed, but hyperlink and the prototype-interaction list were not in the selective Kiwi decoder's field policy, so links carried in .fig files were silently skipped at gate 1. Buttons and linked text therefore never became real anchors.

What changed

• FigKiwiDecoder.php — whitelist hyperlink, prototypeInteractions, reactions, and transitionNodeID on NodeChange, plus the supporting Hyperlink, PrototypeInteraction, PrototypeEvent, and PrototypeAction struct policies needed for the URL/navigation fields to decode. Kiwi names/enum tokens were verified by decoding a real .fig schema chunk (the schema embeds Hyperlink {url, guid}, PrototypeInteraction {event, actions}, PrototypeAction {transitionNodeID, connectionType, connectionURL, navigationType}, ConnectionType {NONE, INTERNAL_NODE, URL, ...}, NavigationType {NAVIGATE, OVERLAY, SWAP, SCROLL_TO}).
• ScenegraphNormalizer.php — the decoded Kiwi shape differs from the REST shape the normalizer was written for, so bridge the gaps without changing behavior:
  • read the Kiwi Hyperlink.guid as a node target (the struct has no REST type field);
  • iterate prototypeInteractions alongside reactions (same list, different name);
  • map PrototypeAction.connectionType (URL/INTERNAL_NODE), connectionURL, navigationType, and the transitionNodeID GUID onto the existing action-link extraction.
• Emitter — unchanged; wrapWithLink() already wraps in <a href>, resolving node navigation to the target frame's page_path (or a # placeholder + link_target_unresolved diagnostic).

Scope boundary (prototype animation)

This is about links — URL and node navigation — not full prototype fidelity. PrototypeAction also carries transition animations, overlay/swap behavior, and variable mutations; those fields are intentionally left undecoded. Full prototype-animation/overlay/swap support is a separate, larger effort.

Tests (real output)

Added to tests/contract/run.php and passing (php tests/contract/run.php):

• a Kiwi-shaped hyperlink URL node emits <a class="figma-link" href="https://..." data-figma-link-type="url">;
• an ON_CLICK prototypeInteractions entry with a URL action emits the same anchor wrapper;
• a binary-Kiwi decode fixture proving the new field policy carries the hyperlink URL, the connection type/URL, the interaction trigger, and the GUID navigation destination through the real generic decoder (gate-1 proof).

Refs #328.

AI assistance

• AI assistance: Yes
• Tool(s): Claude Sonnet 4.6 via Claude Code
• Used for: Implementation