Linux X11: no cursor telemetry, so no follow-cursor zoom #1493

Follow-up to #1491 / #1492.

Since #1492, recording works on Linux X11 sessions, but no cursor positions are recorded there: auto-zoom that follows the cursor and the editable cursor overlay are unavailable.

Why: on the browser capture path outside Windows, effectiveBrowserCursorMode (src/hooks/useScreenRecorder.ts) forces system, because Chromium bakes the real cursor into the X11 frames. Keeping editable-overlay would draw a second cursor on top. Cursor positions are only recorded in editable-overlay mode, on every platform.

Possible directions

• Exclude the cursor from the X11 capture (e.g. getDisplayMedia with cursor: "never", if Chromium honours it on X11 — unverified), then lift the system override there.
• Record cursor positions in system mode too (for follow-cursor zoom), without drawing an overlay.

Wayland, macOS and Windows are not affected.