Report unavailable protocols and services; send combos as real keys

Diagnostics collects what this session doesn't allow, logs it, and lists
it in the settings panel (with a dot on the gear): KWin not launching
sloposk as its keyboard (detected by WAYLAND_SOCKET, since KWin offers the
input-method global to every client), fake input missing or too old,
org.kde.keyboard unreachable, and the D-Bus control name taken.

Modifier combos go through fake input even in text fields: KWin drops
the input method's modifier mask for most clients, so Ctrl+A typed "a".

The desktop file is generated with an absolute Exec, which KWin needs to
match it: one for the installed binary, one for the build's.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

data/org.sloposk.keyboard.desktop.in

@@ -1,10 +1,11 @@
 [Desktop Entry]
 Name=sloposk
 Comment=iPad-style floating on-screen keyboard
-Exec=sloposk
+Exec=@SLOPOSK_EXEC@
 Type=Application
 Icon=input-keyboard-virtual
 NoDisplay=true
 X-KDE-Wayland-VirtualKeyboard=true
-# Key events for windows without a text field (fake input is restricted).
+# Key events for windows without a text field and held keys (fake input is
+# restricted). KWin matches Exec by absolute path, so it must not be bare.
 X-KDE-Wayland-Interfaces=org_kde_kwin_fake_input