Phone portrait: the 3D model fills the space under the camera and the status strip, and both are always visible together #274

From #50 (owner, 2026-10-20 23:05Z: "3d model control on the bottom and the camera view on top"). On main the camera is pinned on top (#187) but #touch (one-joint lever) takes the space below it.

Done:

• [ ] At 390x844 and 412x915 portrait: camera on top (16:9, full width), the 3D model canvas directly below it down to the bottom bar.
• [ ] The camera box and the model box never overlap and neither is hidden; a test checks their boxes (same style as src/stop-layout.test.ts).
• [ ] Desktop and landscape layouts unchanged.
• [ ] forge.json untouched. bun --cwd Software/so101 test passes.

Files: Software/so101/src/viewer.html, src/ui/mobile.css. Layout only: the slider tray (separate issue) and touch drag are not part of this.