SteamOS NVIDIA Installer 0.1.7

Two fixes for the desktop, and the update window fits the screen again. Nothing
compiled changed, so Installer Update delivers all of it and no new image is
needed.

• The update confirmation window can be answered again. Zenity grows a dialog
  to fit its text and ignores a requested height, so the previous release's notes
  pushed Continue and Cancel off the bottom of a 1440p screen and the window could
  not be dismissed at all. It now shows the first lines, says how many are left
  and points at the release page.

• Steam in Desktop Mode gets the same environment as Game Mode. Game Mode
  starts Steam as steam-launcher.service, the KDE desktop starts it as an
  instance of app-steam@.service, and everything this project adds hung off the
  first one only. Outgoing Remote Play from the desktop therefore encoded on the
  CPU with libx264 while the hardware encoder sat idle, because Valve's
  /etc/profile.d/libva.sh forces a driver name written for AMD hardware. Both
  drop-ins are now written for both launchers from one loop, and the wrong driver
  name is removed for Steam. Measured on hardware: the desktop now reports
  Desktop PipeWire NV12 + VAAPI HEVC where it reported libx264 before.

Known and not fixed here: receiving a stream in Desktop Mode still needs hardware
decoding switched off in Steam's own settings. With it on, Steam's client picks a
decode path that costs 153 ms per frame instead of the one it uses under
Gamescope, and rebuilds its decoder three to four times a second rather than
decoding. Software decoding measures 1.66 ms per frame and 43 frames per second on
the same machine, and Game Mode is unaffected. The receiver driver behaves
identically in both modes and a different client decodes in hardware on the same
desktop, so this is not something this project can fix. See the Troubleshooting
page.

Validation. Both changes were exercised on an RTX 5060 with NVIDIA 610.57.04 on
SteamOS 3.8.28. The source tree passes its suite on Linux.