Add DISABLE_WINDOW_BUTTONS to remove all titlebar buttons

[junkerderprovinz]

Closes #186.

DISABLE_WINDOW_BUTTONS=true removes minimize, maximize and close from the titlebar. The two new blocks sit next to the existing DISABLE_CLOSE_BUTTON ones: they strip I, M and C from the openbox titleLayout, and iconify, max and close from the labwc layout. The labwc match works on the tokens rather than on the default string, so it still ends at icon: when DISABLE_CLOSE_BUTTON has already taken close out.

This only covers the buttons. The titlebar mousebinds are unchanged, so double-clicking the openbox titlebar still toggles maximize.

I left HARDEN_OPENBOX alone so existing kiosk setups keep the titlebar they have now. If you'd rather it turned this on too, that's one more export next to DISABLE_CLOSE_BUTTON, and I can add it.

Tested on the published debiantrixie image with this run mounted over the original, under X11 and with PIXELFLUX_WAYLAND=true, each with and without HARDEN_OPENBOX:

openbox  <titleLayout>NLMC</titleLayout>          ->  <titleLayout>NL</titleLayout>
labwc    <layout>icon:iconify,max,close</layout>  ->  <layout>icon:</layout>

With HARDEN_OPENBOX, the locked rc.xml under /config ends up the same. In the web client the titlebar shows no buttons, while the same image without the variable still draws all three.

The run file is identical on alpine324, arch, dev, fedora44, kali and ubunturesolute. On the alpine324 image, which uses busybox sed, the same four runs give the same result.

Once this lands I'll add the variable to the switch tables on the selkies security.md and building-images.md pages in docker-documentation.

[thelamer]

Can you pr this against dev? In general dev stuff will all get ported over to all the flavors in bulk when we are ready for a waterfall.

[thelamer]

implemented in dev