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/process-management.md

@@ -114,7 +114,7 @@ the architecture layer calls up into `tick`.
 - ~~There is no exit status in the notification~~ Closed (M17.2): the kernel
   records how every process ends — exited, a fault class, or killed — before it
   posts the exit notification, and the supervisor reads it with
-  `process_exit_reason` (`runtime.process.exitReason`). This is the input to
+  `process_exit_reason` (`process.exitReason`). This is the input to
   restart policy ([process-lifecycle.md](process-lifecycle.md)); an exit *code*
   for the clean case can still ride alongside later.
 - Enumerate writes through the caller's raw pointer under the bring-up trust