feat(sddm): add fws login theme for kde xfce and hyprland

Introduce a new SDDM theme "fws" designed for FWS with support for KDE, XFCE, and Hyprland desktop environments.

The theme is built using pure QtQuick and QtQuick.Controls (Basic style) with no additional dependencies beyond what SDDM already requires. It includes:

- Main.qml: Custom login screen with clock, date, user/password fields, session selector, and power controls
- metadata.desktop: Theme metadata and configuration
- theme.conf: Default configuration with customizable accent color and gradient colors

The design uses a dark theme with accent colors and supports capslock detection and login error handling.

configs/releng/airootfs/usr/share/sddm/themes/fws/metadata.desktop

@@ -0,0 +1,17 @@
+[SddmGreeterTheme]
+Name=FWS
+Description=Écran de connexion FWS
+Author=FWS
+Copyright=FWS
+License=GPL-2.0-or-later
+Type=sddm-theme
+Version=1.0
+Website=
+Screenshot=
+MainScript=Main.qml
+ConfigFile=theme.conf
+TranslationsDirectory=
+Email=
+Theme-Id=fws
+Theme-API=2.0
+QtVersion=6