fix: restore camera when screen-picker is canceled

[JohnMcLear]

Summary

Clicking the screenshare button when the camera is on, then clicking Cancel in the OS screen-picker, used to leave the user with no video at all (camera button stuck off, stale disabled camera track in the local stream).

Bug

addAsyncEventHandlers($screenshareBtn, ...) in static/js/index.js did:

this._selfViewButtons.video.enabled = false;            // turn camera button off
this._selfViewButtons.screenshare.enabled = true;
await this.updateLocalTracks({updateVideo: true});      // calls getDisplayMedia

If getDisplayMedia rejects (user clicks Cancel → NotAllowedError, or browser denies):

• updateLocalTracks flips screenshare.enabled back to false.
• But the camera button is still off (we set it sync, before the await).
• The OLD camera track in _localTracks.stream is now disabled (loop on line 692-694 sets track.enabled = video.enabled which is false).
• User sees: both buttons off, no video, but camera light may still be on (track is live but disabled).

Fix

Capture the camera's previous state. After updateLocalTracks, if the user wanted to enable screenshare and screenshare didn't take and the camera was on before, re-enable the camera button and call updateLocalTracks({updateVideo: true}) once more so the camera track ends up enabled + live again.

Test

New static/tests/frontend-new/specs/screenshare.spec.ts:

• Camera-on scenario: stub getDisplayMedia to throw NotAllowedError → click screenshare → assert camera button on, screenshare button off, video track live + enabled.
• Camera-off scenario: turn camera off, click screenshare, cancel → assert both buttons stay off (we don't auto-enable a camera the user explicitly turned off).

Couldn't run locally — my etherpad-lite checkout is on a feature branch whose playwright.config.ts doesn't auto-discover plugin specs. CI on develop has the right test-match config.

Semver: patch

Bug fix.

Test plan

• CI: new screenshare.spec.ts passes (2 cases) and existing suite stays green
• Manual smoke: pad with camera enabled → click screenshare button → click Cancel in picker → camera should still show live video, camera button should be on, screenshare button should be off

🤖 Generated with Claude Code

[JohnMcLear]

/review

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