fix: make portal startup uwsm-aware to stop light-mode race

Logging in via a bare Hyprland session never activates
graphical-session.target, so the systemd xdg-desktop-portal units can't
start. The old script worked around this by killing and relaunching the
portals manually, but that delayed the portal past waybar/chromium
startup, so they intermittently came up in light mode.

Switch to the "Hyprland (uwsm-managed)" session: uwsm activates
graphical-session.target and systemd starts the portals in the right
order. The startup script now detects that target and bows out, falling
back to the manual launch only on a bare session (e.g. another machine
without uwsm). Document uwsm in the README.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

hypr/scripts/xdg-desktop-portal-hyprland.sh

@@ -1,8 +1,23 @@
 #!/bin/sh
 
-sleep 1
-killall -e xdg-desktop-portal-hyprland
-killall xdg-desktop-portal
+# Under a uwsm-managed session, systemd brings up graphical-session.target and
+# starts the xdg-desktop-portal units natively, in the right order. In that case
+# we must NOT manually kill/relaunch them — doing so fights systemd and causes
+# the portal to crash (broken pipe), which left apps stuck in light mode.
+#
+# So: wait briefly for graphical-session.target. If it comes up (uwsm), bow out.
+# If it never does (a bare "Hyprland" session, e.g. launched directly from GDM),
+# fall through and start the portals manually as before.
+for _ in $(seq 1 10); do
+    if systemctl --user -q is-active graphical-session.target; then
+        exit 0
+    fi
+    sleep 0.5
+done
+
+# Bare session fallback: start the portals by hand.
+killall -e xdg-desktop-portal-hyprland 2>/dev/null
+killall xdg-desktop-portal 2>/dev/null
 /usr/lib/xdg-desktop-portal-hyprland &
 sleep 2
 /usr/lib/xdg-desktop-portal &