packaging/windows: fix BTRFS+QEMU boot-loop, document what's confirmed

Real issue hit on a real run: dockur/windows warns about BTRFS storage
but it's not idle -- on this host it boot-looped Windows Setup for
hours (same log lines repeating forever, disk barely growing), a known
bad combination for QEMU disk images on a copy-on-write filesystem.
build_windows.sh now disables COW on storage/ itself (chattr +C,
harmless no-op on non-btrfs or an already-populated dir from a prior
run). README updated to reflect both real fixes now confirmed needed
on this host (this one, plus the earlier SELinux :Z mount fix) instead
of the original "written but never run" status.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packaging/windows/README.md

@@ -6,12 +6,28 @@ machine and no GitHub, by booting a real Windows VM inside a container
 hood, no license key needed for the eval install it fetches automatically)
 and driving the whole build over a shared folder.
 
-**Status: written, not yet run against a real boot.** Everything here
-follows dockur/windows's and WiX's documented mechanics, but there's no
-KVM/Windows available in the environment this was authored in to actually
-exercise it end to end. Treat the first run as a debugging session, not a
-push-button success — watch it happen at http://localhost:8006 (dockur's
-noVNC viewer) so you can see where it's stuck if it stalls.
+**Status: has actually been run.** Two real environment issues hit and
+fixed so far (both already applied in this directory, see "Confirmed
+issues hit" below); Windows install itself was still in progress as of
+last check. `oem/install.bat` onward (MSYS2/GTK4/WiX provisioning, the
+actual .msi packaging) has NOT been reached/exercised yet — treat that
+part as still a debugging session, not a push-button success. Watch it
+happen at http://localhost:8006 (dockur's noVNC viewer) if it stalls.
+
+## Confirmed issues hit (on Fedora + BTRFS)
+
+- **SELinux blocks the bind mounts** ("Storage folder (/storage) is not
+  writeable!") — fixed with `:Z` on every volume in `docker-compose.yml`.
+  Harmless no-op on a host without SELinux.
+- **BTRFS + QEMU disk images boot-loop Windows Setup for hours** with no
+  error, just the same boot-manager log lines repeating forever and the
+  disk barely growing — dockur/windows warns about this itself
+  ("you are using the BTRFS filesystem for /storage, this might
+  introduce issues with Windows Setup!"), and on this host it wasn't
+  idle chatter. Fixed by disabling copy-on-write on `storage/` before
+  the VM ever writes to it (`chattr +C`, only affects files created
+  after it's set, so it needs an empty directory) — `build_windows.sh`
+  now does this itself on every run. No-op on a non-btrfs filesystem.
 
 ## How it fits together