feat(annotate): open local image links in an HTML page in the image lightbox

[backnotprop]

What

In a raw-HTML annotate session, a link to a local image (<a href="renders/home-1440.png"><img …></a>) used to toast "Can't open home-1440.png — Only markdown, text and HTML documents open in Plannotator." It now opens in the existing image lightbox.

How

• resolveHtmlLinkIntent (packages/ui/utils/htmlLinkNavigation.ts) has a new { kind: "image", path, url, label } intent for relative and root-relative links to png jpg jpeg gif webp svg avif bmp ico apng (the code-review preview set, isReviewImagePath). The url is the page's own /api/html-assets/<token>/… route, read from the <base href> the server already installs (htmlAssetRouteFromDocument). So the lightbox reads only what the page itself can load. Nothing new becomes readable.
• Containment: an image is shown only when it resolves inside the current page's directory (the token root). If it resolves outside (../x.png, or a root-relative path outside a linked page's folder), a toast says "Images open only from this page's own folder." unsupported now carries a reason (type / outside-asset-root / no-asset-root). External http(s) image URLs still open in a new tab.
• Lightbox: extracted from Viewer.tsx to packages/ui/components/ImageLightbox.tsx. The Viewer and App both mount it. It shows the image only through <img src>. When it opens it takes focus, which pulls focus out of the iframe. While open, it swallows keys on the window capture phase, so:
  • Esc closes it before the HTML Esc ladder runs.
  • Mod+Enter cannot submit a decision behind it. This also fixes the markdown lightbox, which did not block it before.
• Armed vs Interact: unchanged. The bridge already decides this for every link. Armed clicks pin the element. Interact opens the lightbox.
• Server: no route changes. .bmp is added to the shared asset content-type table (packages/shared/html-assets.ts, vendored to Pi), so the whole preview set serves. Without it, .bmp returned 415.

Verified

• Typecheck. Full bun test: the only failure was the DOM allowlist, fixed by adding the new DOM test to test.yml.
• New tests:
  • The image intent, root containment, encoding, no-asset-root, external images and parsing the asset route.
  • The prefix is pinned against the server constant.
  • A DOM test that the lightbox keeps Esc and Mod+Enter from reaching window listeners.
• bun run --cwd apps/review build && bun run build:hook, and packages/ui smoke:package.
• Live: a CLI compiled from this branch (temp PLANNOTATOR_DATA_DIR, headless Chromium):
  • Armed: clicking the thumbnail opened the comment composer and no lightbox.
  • Interact: clicking it showed the full 800×500 PNG from /api/html-assets/<token>/renders/x.png, with focus on the lightbox.
  • With the lightbox open, Meta+Enter and Ctrl+Enter posted no decision.
  • Esc closed the lightbox and the surface stayed in Interact.
  • The ../outside.png link showed the out-of-folder toast.