docs: catch the build docs up with the package split

Review findings: the plan doc claimed no implementation existed, had the
domain dependency order wrong (kernel depends on protocol; device on
kernel + protocol + csv), never placed the three shared contracts, and
named a nonexistent new-driver-checklist.md. Its status now records the
implemented phases (and the deliberate pci-bus-first pilot), the target
shape carries the contract placements and the path-dependency-only
constraint on the kernel package's out-of-root abi export, and the
execution notes describe the post-pilot build for whichever session
runs the remaining waves. README's repo layout gains build-support/
and the packages-note; driver-model, threading, system-requirements,
and the two display plan docs stop citing root build.zig for recipe
facts that now live in build-support.

docs/device-driver-development/display-v2-plan.md

@@ -18,9 +18,11 @@ lands on its own and ends in a **verifiable gate** — shaped for a `/loop` run,
 
 Follow [coding-standards.md](../coding-standards.md): spell out non-acronym abbreviations,
 kebab-case file names, no `Co-Authored-By` trailers. New user binaries go through
-`addUserBinary` and get packed into the initial-ramdisk; protocols are
-`b.addModule("…-protocol", …)` imported into `runtime`; new syscalls extend
-[abi.zig](../../system/abi.zig) `SystemCall` + a `library/runtime` wrapper.
+build-support's shared user-binary recipe and get packed into the initial-ramdisk;
+protocols are modules exported by the `library/protocol` package; new syscalls extend
+[abi.zig](../../system/abi.zig) `SystemCall` + a `library/kernel` wrapper.
+(This section predates the build-packages split; see
+[build-packages-plan.md](../build-packages-plan.md) for the current build shape.)
 
 ## How to verify along the way