Existing upload/feed specs seed events straight into the relay, bypassing the
app's own publish path. This spec drives the actual UI: open the upload modal,
switch to External Link mode, fill title + URL, submit -> the app signs and
publishes to the mock relay -> the video appears in the feed; then the owner
deletes it via the gear menu and it leaves the feed.
Closes the launch-readiness coverage gap on the publish lifecycle (the S3/R2
file upload + cleanup are covered by the unit suites). Verified passing on
chromium (2/2).
Co-Authored-By: Claude Opus 4.8 <[email protected]>