feat: Add image position presets and sliders

Introduce image positioning presets and UI improvements for image overlay control. image.py: compute overlay coordinates for top-left/top-right/bottom-left/bottom-right/center positions and respect corner offset and opacity. settings.py: replace spinboxes with horizontal sliders (with value labels and custom style), add Wallpaper Mode checkbox and Position combo, wire controls to state and include them in the settings tab; ensure dialog rollback restores new temp settings. config/config.py & utils/settings.py: persist and load new image_as_wallpaper and image_position settings and extend save_settings to accept them. data/state.py: add new state fields and properties for image_position, custom position flags and x/y coordinates; change default image_as_wallpaper to false. These changes enable preset positioning, improved UX for sizing/offset/opacity, and persistence of new image options.

src/interface/dialogs/image.py

@@ -163,8 +163,20 @@ class Image(QObject):
             self.overlay_label.adjustSize()
             self.overlay_label.raise_()
 
-            x = parent.width() - self.overlay_label.width() - int(state.image_offset)
-            y = parent.height() - self.overlay_label.height() - int(state.image_offset)
+            pos = state.image_position
+            off = int(state.image_offset)
+            w = self.overlay_label.width()
+            h = self.overlay_label.height()
+            if pos == "top-left":
+                x, y = off, off
+            elif pos == "top-right":
+                x, y = parent.width() - w - off, off
+            elif pos == "bottom-left":
+                x, y = off, parent.height() - h - off
+            elif pos == "center":
+                x, y = (parent.width() - w) // 2, (parent.height() - h) // 2
+            else:  # bottom-right (default)
+                x, y = parent.width() - w - off, parent.height() - h - off
 
             self.opacity_effect.setOpacity(state.image_opacity / 100)