UScreen 1.2.1 — USB second monitor for Linux with S Pen support

A day after 1.2.0, because two people found the same real bug on Debian-based systems.

Touch and pen went to the wrong screen on Debian, Ubuntu, Neon, Pika…

The daemon pins the tablet's touch and pen onto the virtual display by setting
a property on KWin over D-Bus, and it did that by running qdbus. On
Debian- and Ubuntu-based Plasma systems that binary usually is not installed:
plain qdbus belongs to Qt5, and Plasma 6 ships qdbus-qt6. Every mapping
call failed, the daemon logged one line about it and carried on, and KWin was
left to place an absolute input device on its own — so touches drove the
laptop's screen, or landed at 0,0, depending on the machine. It looked exactly
like graphics-tablet mode being stuck on. Reported in
#9 and
#10.

KWin is now reached through systemd's busctl, which every distribution this
project targets has, and falls back to qdbus, qdbus6, qdbus-qt6 and
qdbus-qt5 in turn. The same call path carries on-screen-keyboard
suppression, which was silently off on those systems too.

uscreen doctor gained a KWin D-Bus line: it names the tool it reached
KWin with, or fails the check and says what to install. On the affected
machines the Desktop section was simply empty, which told nobody anything.

Wi-Fi in one command

uscreen wifi, run once with the cable plugged in, switches the tablet's adb
to the network, remembers its address and connects. From then on the daemon
retries that address by itself whenever no tablet is on USB, so the tablet
comes back as a screen without anyone typing an adb command
(#8). uscreen wifi --off
undoes it. The video and input ports stay on loopback, reached through adb's
tunnel, so nothing new is exposed to your network. Wi-Fi remains a fallback:
the median latency matches the cable, individual frames do not.

Also

• The settings window tells the desktop it is uscreen, so the KDE task bar
  shows the UScreen icon instead of a generic monitor.
• Installing now refreshes the icon caches, so the menu entry stops being a
  blank sheet until the next login.

Update both halves together. Files: .deb, .rpm, PKGBUILD archive,
portable tarball, uscreen.apk, SHA256SUMS.