Introduce DeviceStore.pas (TDeviceStore) as the single source of truth for
saved devices (hpsdr_devices.ini CRUD + autostart) and the current discovery
list. The controller owns one instance (created/freed in its ctor/dtor);
desktop and (later) web frontends edit/render through it so the lists never
diverge.
Refactor TDeviceDialog to use a TDeviceStore reference instead of its own
arrays + ini code. MainForm wires FDeviceDialog.Store to the controller's
store, routes discovery results (DoAddDevice) and the preload-rate lookup
through it (TDiscoveredDevice now carries the MAC), and drops the now-unused
FDevices/TDeviceItem. Behavior-preserving for the desktop dialog.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
