refactor(adapter-riscv): split kmain into boot/, devices/ modules
kmain is now 20 lines — six function calls:
hardware::init → BSS, MMU, traps, timer, PLIC, kernel
loader::load_init → read init.elf, create process, map ELF
loader::load_server → read server ELF, create process, map ELF
storage_setup → VirtIO block re-init, shared buffer, phys-info
gpu_setup → VirtIO GPU init, framebuffer alloc, phys-info
caps::grant_all → endpoints, capability grants
New modules:
boot/hardware.rs — hardware init (BSS, MMU, traps, kernel)
boot/loader.rs — ELF loading, thread setup, enter_userspace
boot/caps.rs — endpoint creation, capability grants
devices/storage_setup.rs — VirtIO block for storage server
devices/gpu_setup.rs — VirtIO GPU for display server
All unsafe contained in hw/, mmu/, trap/. Boot and device
modules call safe wrappers.