Respect excluded files in output step counts and processing validation

- Output step now shows only included (non-excluded) image count and size
- Navigate-to-step refresh accounts for exclusions
- Process action checks for included images, not just loaded files

pixstrip-gtk/src/steps/step_output.rs

@@ -97,15 +97,20 @@ pub fn build_output_page(state: &AppState) -> adw::NavigationPage {
         .title("Batch Info")
         .build();
 
-    let file_count = state.loaded_files.borrow().len();
-    let total_size: u64 = state.loaded_files.borrow().iter()
+    let excluded = state.excluded_files.borrow();
+    let files = state.loaded_files.borrow();
+    let included_count = files.iter().filter(|p| !excluded.contains(*p)).count();
+    let total_size: u64 = files.iter()
+        .filter(|p| !excluded.contains(*p))
         .filter_map(|p| std::fs::metadata(p).ok())
         .map(|m| m.len())
         .sum();
+    drop(files);
+    drop(excluded);
 
     let count_row = adw::ActionRow::builder()
         .title("Images to process")
-        .subtitle(format!("{} images ({})", file_count, format_size(total_size)))
+        .subtitle(format!("{} images ({})", included_count, format_size(total_size)))
         .build();
     count_row.add_prefix(&gtk::Image::from_icon_name("image-x-generic-symbolic"));