Left-clicking a feed card (Ctrl/Cmd/middle still open youtube.com in a new tab)
opens a modal that plays the video in-app via the YouTube IFrame Player API
instead of leaving the app. Using the JS API (not a bare embed) lets us read the
playback position: it's checkpointed per-video in localStorage and on close, and
restored via the 'start' param when the video is reopened. The modal closes via
a header button, the backdrop, or ESC (ESC only while focus is on our page — a
cross-origin iframe owns its own key events).
