Add all wizard step UIs: workflow, images, resize, convert, compress, metadata, output

Full Adwaita widget-based layouts for all 7 wizard steps with
PreferencesGroups, SwitchRows, SpinRows, ComboRows, FlowBoxes,
ExpanderRows for social media presets, quality slider with named
marks, metadata radio group, and output configuration.

pixstrip-gtk/src/steps/step_output.rs

@@ -0,0 +1,110 @@
+use adw::prelude::*;
+
+pub fn build_output_page() -> adw::NavigationPage {
+    let scrolled = gtk::ScrolledWindow::builder()
+        .hscrollbar_policy(gtk::PolicyType::Never)
+        .vexpand(true)
+        .build();
+
+    let content = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(12)
+        .margin_top(12)
+        .margin_bottom(12)
+        .margin_start(24)
+        .margin_end(24)
+        .build();
+
+    // Operation summary
+    let summary_group = adw::PreferencesGroup::builder()
+        .title("Operation Summary")
+        .description("Review your processing settings before starting")
+        .build();
+
+    let summary_placeholder = adw::ActionRow::builder()
+        .title("No operations configured")
+        .subtitle("Go back and configure your workflow settings")
+        .build();
+    summary_placeholder.add_prefix(&gtk::Image::from_icon_name("dialog-information-symbolic"));
+
+    summary_group.add(&summary_placeholder);
+    content.append(&summary_group);
+
+    // Output directory
+    let output_group = adw::PreferencesGroup::builder()
+        .title("Output Directory")
+        .build();
+
+    let output_row = adw::ActionRow::builder()
+        .title("Output Location")
+        .subtitle("processed/ (subfolder next to originals)")
+        .activatable(true)
+        .build();
+    output_row.add_prefix(&gtk::Image::from_icon_name("folder-symbolic"));
+
+    let choose_button = gtk::Button::builder()
+        .icon_name("folder-open-symbolic")
+        .tooltip_text("Choose output folder")
+        .valign(gtk::Align::Center)
+        .build();
+    choose_button.add_css_class("flat");
+    output_row.add_suffix(&choose_button);
+    output_row.add_suffix(&gtk::Image::from_icon_name("go-next-symbolic"));
+
+    let structure_row = adw::SwitchRow::builder()
+        .title("Preserve Directory Structure")
+        .subtitle("Keep subfolder hierarchy in output")
+        .active(false)
+        .build();
+
+    output_group.add(&output_row);
+    output_group.add(&structure_row);
+    content.append(&output_group);
+
+    // Overwrite behavior
+    let overwrite_group = adw::PreferencesGroup::builder()
+        .title("If Files Already Exist")
+        .build();
+
+    let overwrite_row = adw::ComboRow::builder()
+        .title("Overwrite Behavior")
+        .subtitle("What to do when output file already exists")
+        .build();
+    let overwrite_model = gtk::StringList::new(&[
+        "Ask before overwriting",
+        "Auto-rename with suffix",
+        "Always overwrite",
+        "Skip existing files",
+    ]);
+    overwrite_row.set_model(Some(&overwrite_model));
+
+    overwrite_group.add(&overwrite_row);
+    content.append(&overwrite_group);
+
+    // Image count
+    let stats_group = adw::PreferencesGroup::builder()
+        .title("Batch Info")
+        .build();
+
+    let count_row = adw::ActionRow::builder()
+        .title("Images to process")
+        .subtitle("0 images")
+        .build();
+    count_row.add_prefix(&gtk::Image::from_icon_name("image-x-generic-symbolic"));
+
+    stats_group.add(&count_row);
+    content.append(&stats_group);
+
+    scrolled.set_child(Some(&content));
+
+    let clamp = adw::Clamp::builder()
+        .maximum_size(600)
+        .child(&scrolled)
+        .build();
+
+    adw::NavigationPage::builder()
+        .title("Output & Process")
+        .tag("step-output")
+        .child(&clamp)
+        .build()
+}