The status strip shows '12 here · 4 signed in · 8 watching' from the /live presence frame, with its space reserved so nothing shifts #359

Split from #291, the page half. It builds on the presence frame.

Done:

• [ ] Software/so101/src/ui/lobby-panel.js (or the strip's existing module) renders the presence frame as one line in the status strip, with text set through textContent only. Its row is reserved from the first paint, so the camera box and strip never change height when it arrives.
• [ ] A test: a presence frame renders 'N here · N signed in · N watching', and a frame missing a number or with a non-number is ignored.
• [ ] forge.json is untouched, and bun --cwd Software/so101 test passes, including the first-visit gzip budget.