feat(viewer): routes, radar, presentation and image/video export

[hyamero]

Third of three PRs toward the archify gallery: the viewer features archify has and stackmap lacked. It is stacked on the sequence PR: merge that first, then retarget this PR to main before merging.

• Route (R)
  • Pick two nodes to light every directed path between them.
  • The inspector lists the shortest path; the route is deep-linked as #route=a~b.
  • Replies are left out unless nothing connects without them, so a reply's loop back to its caller doesn't light the whole diagram. A sequence's route follows messages in time.
  • Esc ends the route from any control.
• Radar (M): the minimap draws edges and mirrors the explorer's dimming.
• Presentation (F): full screen, chrome hidden, stepping through Overview and each view with the arrow keys, with a caption bar.
• Export: JPEG and WebP at 2×, and a flow video.
  • The video shows the diagram with a pulse running along each connection in reading order.
  • It is WebM, or MP4 where the browser records only that, and fits within 1920×1080.
  • Failed or empty recordings report an error instead of saving.
  • The menu lists only the formats the browser can encode.

Single-key shortcuts ignore text fields, open menus and key repeat. README and skill are updated.

Reviewed in a fresh context. All Important and Minor findings for this part are fixed, with unit and browser tests.

[github-actions]

🎉 This PR is included in version 0.1.0-rc.1 🎉

The release is available on:

• v0.1.0-rc.1
• GitHub release

Your semantic-release bot 📦🚀

[github-actions]

🎉 This PR is included in version 0.1.0 🎉

The release is available on:

• v0.1.0
• GitHub release

Your semantic-release bot 📦🚀