Prepare for the move to Fedora

tools/posix/setup-fedora.sh installs the toolchain and reports what it
cannot: PowerShell has no Fedora package, and bootcheck is the test
suite, so the script says how to get pwsh rather than failing quietly.
It also checks /dev/kvm, since a Ryzen box can run the tests at native
speed.

docs/moving-to-linux.md is the actual procedure: copy the repo, restore
the memory, install, build. The memory travels inside the repo and
`memory-sync.sh import` puts it under the key this machine derives from
its own path -- /home/nexoniarz/Documents/SchOS becomes
-home-nexoniarz-Documents-SchOS, where D:\DEV\SchOS was D--DEV-SchOS.

OVMF discovery no longer assumes QEMU's Windows layout. Fedora ships
edk2-ovmf to /usr/share/edk2/ovmf/, Debian and Arch differ again, so the
Makefile searches a list and names the packages when it finds nothing.
Tested through the shell rather than $(wildcard): on Windows make is a
native binary using Win32 file calls, while `command -v` returns an MSYS
path like /c/Users/..., which $(wildcard) cannot see -- it returned
nothing on a machine that had the firmware.

Two things only that machine can test: `make ports` builds musl, toybox
and mksh from source, which Windows cannot do at all; and the SchFS
round-trip needs symlinks and hard links, so it has never actually run.

README.md

@@ -81,7 +81,9 @@ Builds on **Linux, macOS, FreeBSD/OpenBSD/NetBSD and Windows** (Git Bash). The
 toolchain is clang + lld everywhere — it is a cross-compiler by construction, so
 one LLVM install targets the bare-metal kernel, the 16-bit boot code and musl
 userland from any host. See **[docs/building.md](docs/building.md)** for
-prerequisites per platform.
+prerequisites per platform, and
+**[docs/moving-to-linux.md](docs/moving-to-linux.md)** for moving a checkout
+between machines.
 
 ## Testing