WSLg native-app integration: export XDG_DATA_DIRS to systemd user-bus

Operator 2026-05-10: "flatpak apps no longer showing in windows as
native apps". Root cause: WSLg's app-list-monitor service scans
XDG_DATA_DIRS for .desktop files and registers them as Windows
Start Menu entries via RDP-RAIL. The systemd-user-bus session
XDG_DATA_DIRS was EMPTY -- so the monitor only found system
/usr/share/applications/*.desktop and missed every flatpak's
exports/share/applications/. Result: zero Windows-side Start Menu
integration for installed flatpak GUI apps (Epiphany, Nautilus,
gnome-software, codium, Flatseal, ExtensionManager).

Fix: mios-wsl-env-import.service now sets + propagates
XDG_DATA_DIRS=/var/home/mios/.local/share/flatpak/exports/share:
/var/lib/flatpak/exports/share:/usr/local/share:/usr/share
into the systemd-user-bus + dbus activation environment.

Order rationale:
  ~/.local first  -- per-user flatpak installs (operator-added)
  /var/lib next   -- system-wide flatpak installs (mios overlay)
  /usr/local      -- standard XDG fallback
  /usr            -- distro vendor desktop files

After the next user-bus startup (or `systemctl --user restart
mios-wsl-env-import.service`), WSLg's monitor discovers all six
of MiOS's bundled flatpaks and registers them as Windows native
apps.

Author: Kabuki94

usr/lib/systemd/user/mios-wsl-env-import.service

@@ -37,8 +37,18 @@ Type=oneshot
 # ConditionEnvironment=XDG_SESSION_CLASS=user".  Force-setting it
 # here unblocks the whole chain.
 ExecStart=/usr/bin/systemctl --user set-environment XDG_SESSION_CLASS=user
-ExecStart=/usr/bin/systemctl --user import-environment XDG_CURRENT_DESKTOP WAYLAND_DISPLAY DISPLAY XDG_SESSION_TYPE XDG_SESSION_CLASS XDG_RUNTIME_DIR PULSE_SERVER
-ExecStart=/usr/bin/dbus-update-activation-environment --systemd XDG_CURRENT_DESKTOP WAYLAND_DISPLAY DISPLAY XDG_SESSION_TYPE XDG_SESSION_CLASS XDG_RUNTIME_DIR PULSE_SERVER
+# XDG_DATA_DIRS must include flatpak's exports/share dirs so WSLg's
+# app-list-monitor sees the flatpak .desktop files and registers them
+# as native Windows Start Menu entries via the RDP-RAIL bridge.
+# Without this, only system /usr/share/applications/*.desktop are
+# discovered -- every installed flatpak (Epiphany, Nautilus, gnome-
+# software, etc.) is invisible to Windows. Operator-flagged
+# 2026-05-10 "flatpak apps no longer showing in windows as native apps."
+# Order: ~/.local first (per-user installs), then /var/lib (system-wide
+# installs), then standard /usr/local/share + /usr/share.
+ExecStart=/usr/bin/systemctl --user set-environment XDG_DATA_DIRS=/var/home/mios/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/share
+ExecStart=/usr/bin/systemctl --user import-environment XDG_CURRENT_DESKTOP WAYLAND_DISPLAY DISPLAY XDG_SESSION_TYPE XDG_SESSION_CLASS XDG_DATA_DIRS XDG_RUNTIME_DIR PULSE_SERVER
+ExecStart=/usr/bin/dbus-update-activation-environment --systemd XDG_CURRENT_DESKTOP WAYLAND_DISPLAY DISPLAY XDG_SESSION_TYPE XDG_SESSION_CLASS XDG_DATA_DIRS XDG_RUNTIME_DIR PULSE_SERVER
 RemainAfterExit=yes
 
 [Install]