Replaces the placeholder shell with a sidebar app in the web Clipbin's look:
a session library, a session timeline (footage, missing and cleaned-up spans,
bookmarks, a draggable clip selection exported on keyframes), clips and
settings. Geist Mono and Lucide icons are embedded. The core gains the
library model and formatting; sample data is opt-in for interface work, and
scripts/rig/screenshot-ui.sh captures each screen headlessly.
Encoders and the segment output are created when the capture source first
has a picture, at its own size (portrait monitors record portrait) unless a
resolution is configured, so nothing is written while waiting for a source.
SPEC.md records both decisions; validation docs cover how sessions should end
when the game closes.