tools: group scripts by what runs them

tools/windows/   .ps1   (pwsh, so usable from Linux and macOS too)
  tools/posix/     .sh
  tools/python/    .py
  tools/           .c and .pl

The .c and .pl files stay at the top level because they are not
host-specific: the build compiles or invokes them on every platform.

Call sites updated in the Makefile, ports/mk/port.mk, docs and the
project memory. The one thing that does not survive a move on its own is
a script deriving the repo root from its own location -- all nine
PowerShell tools used Split-Path $PSScriptRoot -Parent, and memory-sync.sh
used dirname/.., both of which quietly become tools/ one level deeper.
Two levels now.

Two pre-existing Windows failures surfaced while verifying, both real and
neither caused by the move:

  - schfs_fsck.c did not compile under mingw at all: --extract uses
    POSIX mkdir(path,mode), symlink() and link(), none of which mingw
    has. That took the whole tool with it, and `make schfs-check` with
    it. mkdir maps to _mkdir; symlink and link fail loudly rather than
    writing a regular file in their place, because an extracted tree
    that differs from the image while reporting success defeats the
    point of --extract.
  - the round-trip test then failed at `ln -s`, since Git Bash cannot
    create symlinks without developer mode. It skips with a message now.
    Not a fudge: mkschfs's mingw build cannot see a symlink either, so
    the test would have compared a tree with none against an image with
    none and called it a pass -- coverage reporting itself as present
    while being absent.

Verified on Windows: build clean, all seven bootcheck suites green,
make schfs-check passes.

docs/architecture/kernel-history.md

@@ -483,7 +483,7 @@ the user is looking at. That single fact is most of what separates a hobby
 project from a product; every shipping system puts that behind a flag.
 
 `cons_serial_only` already existed for panic, so the fix was to start it *set*.
-Everything still goes out the UART — which is where `tools/bootcheck.ps1` reads
+Everything still goes out the UART — which is where `tools/windows/bootcheck.ps1` reads
 it from, so all five suites kept passing untouched — and `console_takeover()`
 clears it on the first `exec()`, the moment userspace genuinely starts.
 `vga_init` no longer clears the screen, so the splash survives the whole of