frontend: embed 3-min demo video in About the Garden sidebar
AI-Sherpa
ab28fc9
Adds a new "Watch the 3-minute demo" details block below "How it works",
with native <video> sourced from the HF Space LFS. On play, the video
expands to half the viewport via a native <dialog> with a dimmed
::backdrop; pause / outside-click / ESC / close-button returns it to
its compact position with currentTime synced back to the inline copy.
Initial commit: Kintsugi Garden — Build Small Hackathon submission
