Replaced the 3-line TODO no-op with a functional LegacyBackend
that:
1. Enumerates available schemes in /scheme/ (logged at info level)
2. Spawns pcid for PCI bus enumeration on non-ACPI systems
Cross-referenced with Linux 7.1 drivers/pci/probe.c for PCI
device enumeration and arch/x86/kernel/devicetree.c for
non-ACPI device discovery.
Previously the backend was a no-op that logged 'TODO' and did
nothing, leaving non-ACPI systems without any hardware detection.
Red Bear OS
2551784cea