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.

tools/windows/fbshot.ps1

@@ -0,0 +1,115 @@
+# Draw on /dev/fb0 and photograph the result.
+#
+# bootcheck -Fb proves fbinfo *ran* and that the numbers it read back are the
+# ones the bootloader programmed. It cannot prove the pixels landed where they
+# were meant to: a framebuffer written with the wrong stride still reports
+# every byte accepted, and the only symptom is a picture that shears
+# progressively down the screen. That is a thing you have to look at.
+#
+#   tools/fbshot.ps1              gradient through mmap
+#   tools/fbshot.ps1 -Mode bars   colour bars through write()
+
+param(
+    [ValidateSet('fill', 'bars')]
+    [string]$Mode = 'fill',
+    [int]$BootSeconds = 20,
+    [string]$Qemu = (Find-Qemu)
+)
+
+# QEMU, on whichever host this is.
+#
+# PowerShell 7 runs on Linux, macOS and the BSDs as well as Windows, so these
+# scripts are usable from all of them -- but the old default was a hardcoded
+# scoop path under $env:USERPROFILE, which exists on exactly one of those. PATH
+# first, because a package-managed qemu is on it everywhere; the scoop location
+# is only a fallback for the Windows install that does not add itself to PATH.
+function Find-Qemu {
+    $exe = if ($IsWindows -or $env:OS -eq 'Windows_NT') { 'qemu-system-x86_64.exe' }
+           else { 'qemu-system-x86_64' }
+    $onPath = Get-Command $exe -ErrorAction SilentlyContinue
+    if ($onPath) { return $onPath.Source }
+    if ($env:USERPROFILE) {
+        $scoop = Join-Path (Join-Path $env:USERPROFILE 'scoop/apps/qemu/current') $exe
+        if (Test-Path $scoop) { return $scoop }
+    }
+    foreach ($p in @('/usr/bin', '/usr/local/bin', '/opt/homebrew/bin')) {
+        $c = Join-Path $p $exe
+        if (Test-Path $c) { return $c }
+    }
+    throw "qemu-system-x86_64 not found on PATH. Install QEMU, or pass -Qemu <path>."
+}
+
+$ErrorActionPreference = 'Stop'
+# Repo root is two levels up: this script lives in tools/windows/.
+$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
+$hda  = Join-Path $root 'schos.img'
+# The root filesystem. SchFS is the only root there is: the kernel mounts
+# device 1 in forkret() and panics if it is not a SchFS volume, so this is
+# not a choice and there is no -SchFS switch any more. It used to default to
+# build/fs.img, which stopped being bootable the moment SchFS became root.
+$hdb  = Join-Path $root 'build/schfs.img'
+$log  = Join-Path $root 'build/fbshot.log'
+$ppm  = Join-Path $root "build/fb-$Mode.ppm"
+
+Remove-Item -Force $log, $ppm -ErrorAction SilentlyContinue
+
+$monPort = 55556      # not crashshot's 55555, so the two can run back to back
+
+$psi = New-Object System.Diagnostics.ProcessStartInfo
+$psi.FileName = $Qemu
+$psi.Arguments = @(
+    "-drive file=`"$hda`",format=raw,index=0,media=disk"
+    "-drive file=`"$hdb`",format=raw,index=1,media=disk"
+    '-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
+    '-display none'
+    "-chardev stdio,id=c0,logfile=`"$log`""
+    '-serial chardev:c0'
+    "-monitor tcp:127.0.0.1:$monPort,server,nowait"
+) -join ' '
+$psi.RedirectStandardInput = $true
+$psi.UseShellExecute       = $false
+
+Write-Host "==> booting" -ForegroundColor Cyan
+$p = [System.Diagnostics.Process]::Start($psi)
+
+function Send-Line($text) {
+    foreach ($ch in ($text + "`n").ToCharArray()) {
+        $p.StandardInput.Write($ch)
+        $p.StandardInput.Flush()
+        Start-Sleep -Milliseconds 30    # serial has no flow control
+    }
+}
+
+try {
+    Start-Sleep -Seconds $BootSeconds
+    Write-Host "  > fbinfo $Mode" -ForegroundColor DarkGray
+    Send-Line "fbinfo $Mode"
+    Start-Sleep -Seconds 8              # 1.9 MB a pixel at a time is not fast
+
+    Write-Host "==> capturing the framebuffer" -ForegroundColor Cyan
+    $client = New-Object System.Net.Sockets.TcpClient('127.0.0.1', $monPort)
+    $writer = New-Object System.IO.StreamWriter($client.GetStream())
+    $writer.AutoFlush = $true
+    Start-Sleep -Milliseconds 500
+    $writer.WriteLine("screendump $ppm")
+    Start-Sleep -Seconds 2
+    $writer.WriteLine('quit')
+    Start-Sleep -Milliseconds 500
+    $client.Close()
+} finally {
+    if (-not $p.HasExited) { $p.Kill() }
+    Start-Sleep -Milliseconds 800
+}
+
+if (Test-Path $log) {
+    $text = Get-Content $log -Raw
+    $idx = $text.IndexOf('fbinfo')
+    if ($idx -ge 0) { Write-Host $text.Substring($idx) }
+}
+
+if (Test-Path $ppm) {
+    Write-Host "==> $ppm ($((Get-Item $ppm).Length) bytes)" -ForegroundColor Green
+} else {
+    Write-Host 'FAIL: no screendump was produced' -ForegroundColor Red
+    exit 1
+}