sway: screenshots, polkit floating, flatpak dark theme

Screenshots
- Swap xfce4-screenshooter for flameshot + grim/slurp/jq; xfce4 used
  the X11 selection so clipboard didn't round-trip to Wayland clients.
  Print invokes flameshot's editor; Shift/Alt+Print are quick
  grim-based captures via a small wrapper script. Flameshot is now
  autostarted so the first capture isn't slow.

Polkit
- Add for_window rules so the xfce-polkit dialog (and any other polkit
  agent) always opens floating.

Flatpak dark theme
- Write /etc/flatpak/overrides/global with GTK_THEME=Yaru-Blue-dark for
  legacy GTK apps, plus a sway-portals.conf so the Settings portal is
  served by xdg-desktop-portal-gtk (wlr doesn't implement it). That
  lets libadwaita apps see color-scheme=prefer-dark.

cleanup-sway: track the new package set.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ansible/roles/profile_desktop_sway/files/sway-portals.conf

@@ -0,0 +1,4 @@
+[preferred]
+default=gtk
+org.freedesktop.impl.portal.Screenshot=wlr
+org.freedesktop.impl.portal.ScreenCast=wlr

ansible/roles/profile_desktop_sway/tasks/main.yml

@@ -37,6 +37,16 @@
     mode: "0755"
   when: "'sway' in (desktop_sessions_enabled | default([]))"
 
+- name: Configure xdg-desktop-portal backend preferences for sway
+  tags: [packages, services, sway, portal]
+  ansible.builtin.copy:
+    src: sway-portals.conf
+    dest: /etc/xdg/xdg-desktop-portal/sway-portals.conf
+    owner: root
+    group: root
+    mode: "0644"
+  when: "'sway' in (desktop_sessions_enabled | default([]))"
+
 - name: Copy sway desktop dotfiles
   tags: [dotfiles, dotfiles:desktop, sway]
   ansible.builtin.copy: