v1.5.0

Changelog

• a1def50 demo: a sample document that exercises every content-link kind
• b102da2 feat(app): scan content links in the deck's document leaves
• 7d43743 feat(contentlink): let a claiming provider reclaim its key from a Markdown link
• e4ee272 feat(filebrowser): scan content links in the rendered-Markdown preview
• 3172875 fix(contentlink): make RendererOwned mean what it claims, and keep the browser
• 1066ee4 test(contentlink): say which OSC-8 terminator each fixture covers