C6: update docs for the library/kernel + client split

Rewrote the repository-layout and driver-model docs to describe the new tree —
library/kernel (the kernel32-style system library: syscall surface split by
concern), library/device (mmio/model/pci/usb/acpi/driver/block), library/client
(display, input service clients), library/protocol (wire contracts) — and swept
the reference docs off the retired runtime shim:

  runtime.system.*  -> logging.* / time.* / process.* / memory.*
  runtime.dma.* / runtime.shared_memory.* / runtime.allocator -> memory.*
  runtime.ipc/process/time/service/Thread/block/display/input -> the module name
  runtime.device / runtime.device_manager -> driver
  library/runtime/<file>.zig -> its new home (kernel/ client/ device/)

docs/README.md (repository layout + source map), docs/driver-model.md (the module
graph + import lists), and the concern/reference docs (ipc, threading, timers,
logging, power, process-lifecycle, device-manager, display, vdso, sysv, drivers,
input, vfs-protocol, coding-standards, ...) now reflect the split. "runtime" that
remains is the userspace-library *concept*, which is still accurate.

The historical plan docs (display-plan, display-v2-plan, threading-plan) and the
zig-self-hosting design note are left as point-in-time snapshots.

docs/sysv.md

@@ -90,9 +90,9 @@ process) instead of silently corrupting the image
 (`buildEntryStack` in `system/kernel/process.zig`); `argv[0]` is always the path
 or initial-ramdisk name the process was spawned as, and `system_spawn`'s optional
 argument blob becomes `argv[1..]`. The runtime's `_start`
-(`library/runtime/start.zig`) hands the block to `rt_start`, which builds a
-`runtime.process.Init` from it and passes that to the program's `main`
-(`pub fn main(init: runtime.process.Init)`; a parameterless `main()` is also
+(`library/kernel/start.zig`) hands the block to `rt_start`, which builds a
+`process.Init` from it and passes that to the program's `main`
+(`pub fn main(init: process.Init)`; a parameterless `main()` is also
 accepted). A C runtime's `crt0` would walk
 the identical layout unmodified — that's the compatibility being bought. The
 `args` test proves the round trip.