Add rename template presets and watermark color picker

- Rename step: quick-fill buttons for common patterns (Date+Name,
  EXIF Date+Name, Sequential, Dimensions, Camera+Date, Web-safe)
- Watermark step: color picker in advanced options using ColorDialogButton
- Add watermark_color field to JobConfig, wire through to core

pixstrip-gtk/src/steps/step_watermark.rs

@@ -315,6 +315,29 @@ pub fn build_watermark_page(state: &AppState) -> adw::NavigationPage {
         .expanded(state.detailed_mode)
         .build();
 
+    // Text color picker
+    let color_row = adw::ActionRow::builder()
+        .title("Text Color")
+        .subtitle("Color of the watermark text")
+        .build();
+
+    let initial_color = gtk::gdk::RGBA::new(
+        cfg.watermark_color[0] as f32 / 255.0,
+        cfg.watermark_color[1] as f32 / 255.0,
+        cfg.watermark_color[2] as f32 / 255.0,
+        cfg.watermark_color[3] as f32 / 255.0,
+    );
+    let color_dialog = gtk::ColorDialog::builder()
+        .with_alpha(true)
+        .title("Watermark Text Color")
+        .build();
+    let color_button = gtk::ColorDialogButton::builder()
+        .dialog(&color_dialog)
+        .rgba(&initial_color)
+        .valign(gtk::Align::Center)
+        .build();
+    color_row.add_suffix(&color_button);
+
     let opacity_row = adw::SpinRow::builder()
         .title("Opacity")
         .subtitle("0.0 (invisible) to 1.0 (fully opaque)")
@@ -347,6 +370,7 @@ pub fn build_watermark_page(state: &AppState) -> adw::NavigationPage {
         .adjustment(&gtk::Adjustment::new(20.0, 1.0, 100.0, 1.0, 5.0, 0.0))
         .build();
 
+    advanced_expander.add_row(&color_row);
     advanced_expander.add_row(&opacity_row);
     advanced_expander.add_row(&rotation_row);
     advanced_expander.add_row(&tiled_row);
@@ -424,6 +448,19 @@ pub fn build_watermark_page(state: &AppState) -> adw::NavigationPage {
             jc.borrow_mut().watermark_opacity = val;
         });
     }
+    // Wire color picker
+    {
+        let jc = state.job_config.clone();
+        color_button.connect_rgba_notify(move |btn| {
+            let c = btn.rgba();
+            jc.borrow_mut().watermark_color = [
+                (c.red() * 255.0) as u8,
+                (c.green() * 255.0) as u8,
+                (c.blue() * 255.0) as u8,
+                (c.alpha() * 255.0) as u8,
+            ];
+        });
+    }
     // Wire image chooser button
     {
         let jc = state.job_config.clone();