Refactor GDM module to correspond SOLID principles

- I don't know how I will support this hell ahh code;
- Added some methods to gnome_shell_theme_builder.py;
- Added "color" property "install" method from theme_base.py.

scripts/utils/global_theme/gdm_theme_prepare.py

@@ -0,0 +1,66 @@
+from scripts.utils import remove_keywords, remove_properties
+from scripts.utils.files_labeler import FilesLabeler
+from scripts.utils.theme.theme import Theme
+
+
+class GDMThemePrepare:
+    """
+    Prepares theme files for installation into the GDM system.
+
+    This class handles:
+    - Theme file labeling for dark/light variants
+    - CSS property and keyword removal for customization
+    - Theme installation with color adjustments
+    """
+    def __init__(self, theme: Theme, theme_file: str, label: str = None):
+        """
+        :param theme: The theme object to prepare
+        :param theme_file: Path to the original decompiled CSS file
+        :param label: Optional label for the theme (e.g. "dark", "light")
+        """
+        self.theme = theme
+        self.theme_file = theme_file
+        self.label = label
+
+    def label_theme(self):
+        """
+        Label the theme files if the label is set.
+        Also updates references in the theme files.
+        :raises ValueError: if the label is not set
+        """
+        if self.label is None:
+            raise ValueError("Label is not set for the theme.")
+
+        files_labeler = FilesLabeler(self.theme.temp_folder, self.theme.main_styles)
+        files_labeler.append_label(self.label)
+
+    def remove_keywords(self, *args: str):
+        """Remove specific keywords from the theme file"""
+        remove_keywords(self.theme_file, *args)
+
+    def remove_properties(self, *args: str):
+        """Remove specific properties from the theme file"""
+        remove_properties(self.theme_file, *args)
+
+    def prepend_source_styles(self, trigger: str):
+        """
+        Add source styles and installation trigger to the theme file.
+
+        This adds original theme styles and a marker that identifies
+        the theme as installed by this application.
+
+        :param trigger: String marker used to identify installed themes
+        """
+        with open(self.theme_file, 'r') as gnome_theme:
+            gnome_styles = gnome_theme.read() + trigger
+            self.theme.add_to_start(gnome_styles)
+
+    def install(self, hue: int, color: str, sat: int | None, destination: str):
+        """
+        Install the theme to the specified destination
+        :param hue: Hue value for the theme
+        :param color: Color name for the theme
+        :param sat: Saturation value for the theme
+        :param destination: Destination folder for the theme
+        """
+        self.theme.install(hue, color, sat, destination=destination)