fix(portal): screen-capture script, portal backend, swaync autostart

screen-capture.sh was a single non-executable line containing a `slur` typo,
so it never ran and nothing referenced it; rewritten as a working region
capture to ~/Pictures plus clipboard.

xdg-desktop-portal/portals.conf pins the wlr backend for sway, and swaync is
pulled in via graphical-session.target.wants so the portal's
Requisite=graphical-session.target is satisfied (the reason screen sharing
previously never started).

.config/sway/scripts/screen-capture.sh

@@ -1,3 +1,33 @@
-#!/bin/bash
+#!/bin/sh
+# Region screenshot -> ~/Pictures + clipboard.
+#
+# This file used to contain a single broken line (`slur`, and it was not
+# executable): the typo meant `slurp` never ran, and nothing referenced it
+# anyway -- the $mod+shift+p keybind in config.d/keybinds has its own inline
+# pipeline. Fixed and kept as the shared implementation so the behaviour is
+# identical wherever it gets wired up.
+#
+# Usage: screen-capture.sh [region|output|full]   (default: region)
+# (no "window" mode: slurp offers region, `-o` output and `-p` point selection
+#  only -- it cannot pick a window)
 
-slur
+set -u
+
+outdir="${XDG_PICTURES_DIR:-$HOME/Pictures}"
+mkdir -p "$outdir"
+file="$outdir/$(date +%F-%H%M%S).png"
+
+case "${1:-region}" in
+    region) geom=$(slurp) || exit 1                       # Esc cancels
+            [ -n "$geom" ] || exit 1
+            grim -g "$geom" "$file" ;;
+    output) geom=$(slurp -o -f '%g') || exit 1            # pick a monitor
+            [ -n "$geom" ] || exit 1
+            grim -g "$geom" "$file" ;;
+    full)   grim "$file" ;;
+    *)      echo "usage: $(basename "$0") [region|output|full]" >&2; exit 2 ;;
+esac
+
+[ -s "$file" ] || { echo "capture failed" >&2; exit 1; }
+wl-copy < "$file"
+notify-send -i "$file" "Screenshot saved" "$file"