Replace watermark position dropdown with visual 3x3 grid

- 9-point position grid using ToggleButtons in a Grid layout
- Visual feedback with radio-checked/radio-symbolic icons
- Position label below grid shows current selection name
- Much better UX than ComboRow for spatial position selection

pixstrip-gtk/src/steps/step_watermark.rs

@@ -94,7 +94,7 @@ pub fn build_watermark_page(state: &AppState) -> adw::NavigationPage {
     image_group.add(&image_path_row);
     content.append(&image_group);
 
-    // Position grid (9-point)
+    // Visual 9-point position grid
     let position_group = adw::PreferencesGroup::builder()
         .title("Position")
         .description("Choose where the watermark appears on the image")
@@ -106,14 +106,62 @@ pub fn build_watermark_page(state: &AppState) -> adw::NavigationPage {
         "Bottom Left", "Bottom Center", "Bottom Right",
     ];
 
-    let position_row = adw::ComboRow::builder()
-        .title("Watermark Position")
+    // Build a 3x3 grid of toggle buttons
+    let grid = gtk::Grid::builder()
+        .row_spacing(4)
+        .column_spacing(4)
+        .halign(gtk::Align::Center)
+        .margin_top(8)
+        .margin_bottom(8)
         .build();
-    let position_model = gtk::StringList::new(&position_names);
-    position_row.set_model(Some(&position_model));
-    position_row.set_selected(cfg.watermark_position);
 
-    position_group.add(&position_row);
+    // Create a visual "image" area as background context
+    let grid_frame = gtk::Frame::builder()
+        .halign(gtk::Align::Center)
+        .build();
+    grid_frame.set_child(Some(&grid));
+
+    let mut first_button: Option<gtk::ToggleButton> = None;
+    let buttons: Vec<gtk::ToggleButton> = position_names.iter().enumerate().map(|(i, name)| {
+        let btn = gtk::ToggleButton::builder()
+            .tooltip_text(*name)
+            .width_request(48)
+            .height_request(48)
+            .build();
+
+        // Use a dot icon for each position
+        let icon = if i == cfg.watermark_position as usize {
+            "radio-checked-symbolic"
+        } else {
+            "radio-symbolic"
+        };
+        btn.set_child(Some(&gtk::Image::from_icon_name(icon)));
+        btn.set_active(i == cfg.watermark_position as usize);
+
+        if let Some(ref first) = first_button {
+            btn.set_group(Some(first));
+        } else {
+            first_button = Some(btn.clone());
+        }
+
+        let row = i / 3;
+        let col = i % 3;
+        grid.attach(&btn, col as i32, row as i32, 1, 1);
+
+        btn
+    }).collect();
+
+    position_group.add(&grid_frame);
+
+    // Position label showing current selection
+    let position_label = gtk::Label::builder()
+        .label(position_names[cfg.watermark_position as usize])
+        .css_classes(["dim-label"])
+        .halign(gtk::Align::Center)
+        .margin_bottom(4)
+        .build();
+    position_group.add(&position_label);
+
     content.append(&position_group);
 
     // Advanced options
@@ -200,10 +248,26 @@ pub fn build_watermark_page(state: &AppState) -> adw::NavigationPage {
             jc.borrow_mut().watermark_font_size = row.value() as f32;
         });
     }
-    {
+    // Wire position grid buttons
+    for (i, btn) in buttons.iter().enumerate() {
         let jc = state.job_config.clone();
-        position_row.connect_selected_notify(move |row| {
-            jc.borrow_mut().watermark_position = row.selected();
+        let label = position_label.clone();
+        let names = position_names;
+        let all_buttons = buttons.clone();
+        btn.connect_toggled(move |b| {
+            if b.is_active() {
+                jc.borrow_mut().watermark_position = i as u32;
+                label.set_label(names[i]);
+                // Update icons
+                for (j, other) in all_buttons.iter().enumerate() {
+                    let icon_name = if j == i {
+                        "radio-checked-symbolic"
+                    } else {
+                        "radio-symbolic"
+                    };
+                    other.set_child(Some(&gtk::Image::from_icon_name(icon_name)));
+                }
+            }
         });
     }
     {