A page kept its ruler guides in `NodeKind::Page`, and since frame guides
(#70) every layer also has its own `guides` field. Both are written as
`guides`, and on reading the layer's own field takes the key, so:
- a reopened page's guides landed in the layer field and were not drawn;
- saving that page wrote `guides` twice (the page kind's list, always
written, then the layer's), and the file no longer opened ("duplicate
field `guides`").
Every layer, pages included, now keeps its guides in the one layer field;
the key in the file is unchanged, so existing files open with their guides.
The field reads every `guides` list a layer has, so files already saved
with the key twice open again with both lists, in file order. This also
covers collab `Create` payloads from older peers.
Regressions: JSON round trips of page and frame guides, a page with two
lists, a bad list still refused (doc); save, reopen, save, reopen through
`.figcraft` and a document.json with the key twice (format). Checked in the
app over the control channel: guides drawn after two save/reopen cycles, and
a file with the key twice opens with all its guides.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LvG6Dyzof21BCrUsByhx2w
