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/device-manager.md

@@ -22,7 +22,7 @@ for drivers.
 How processes stop, reload, and report their deaths is deliberately **not** in this
 document: that is the universal lifecycle every danos process speaks —
 [process-lifecycle.md](process-lifecycle.md), signals over IPC and the stable
-`runtime.process` interface. The device manager is that design's first serious
+`process` interface. The device manager is that design's first serious
 customer, not its owner. Its own protocol contains nothing lifecycle-shaped; a
 driver is stopped, health-checked, and buried exactly like any other process.
 
@@ -137,7 +137,7 @@ way.
 
 Increments 1–4 are the lifecycle prerequisites and live in
 [process-lifecycle.md](process-lifecycle.md) (claim cleanup on death, exit reasons,
-published exit events, signals + `runtime.process`). On top of those:
+published exit events, signals + `process`). On top of those:
 
 5. **device-manager-protocol**: `hello`, supervised spawn with restart policy;
    usb-xhci-bus becomes the first conforming driver.