WIP Add camera probe, compact UI and scrolling

Introduce a CameraProbeWorker to perform quick open/close device probes and populate detected_resolution/detected_fps in the working model (writes into backend namespace and respects fast_start). Add UI improvements: compact two-field rows, read-only Detected res/FPS labels, grouped controls (Resolution, Capture, Analog), and device id wrapping. Replace the right column with a QScrollArea to prevent layout squishing and lock scroll contents to the viewport width via eventFilter. Wire up probe lifecycle (start on camera add, progress/success/error/finished handlers) and update labels when probe results are available. Misc: minor layout/policy tweaks, preview group sizing, and ensure probe skips when preview loader is active.

Author: C-Achard