reorg: relocate device/service clients (C3/C4)
- device.zig + device-manager.zig -> library/device/driver/driver.zig (module
"driver"): the driver author's whole interface — device access (claim/mmioMap/
irqBind/...) plus the device-manager hello() handshake, folded into one import.
- block.zig -> library/device/block/block.zig (a device type).
- display.zig/input.zig -> library/client/{display,input}/ (userspace-service
clients — they talk to services, not the kernel).
build.zig module graph updated; the runtime shim now maps runtime.device and
runtime.device_manager onto "driver", so consumers stay untouched (migrated in C2).
zig build green; driver-restart, usb-storage, display-native, input pass.
dded46726b