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_images.rs

@@ -0,0 +1,142 @@
+use adw::prelude::*;
+
+pub fn build_images_page() -> adw::NavigationPage {
+    let stack = gtk::Stack::builder()
+        .transition_type(gtk::StackTransitionType::Crossfade)
+        .build();
+
+    // Empty state - drop zone
+    let empty_state = build_empty_state();
+    stack.add_named(&empty_state, Some("empty"));
+
+    // Loaded state - thumbnail grid (placeholder for now)
+    let loaded_state = build_loaded_state();
+    stack.add_named(&loaded_state, Some("loaded"));
+
+    stack.set_visible_child_name("empty");
+
+    adw::NavigationPage::builder()
+        .title("Add Images")
+        .tag("step-images")
+        .child(&stack)
+        .build()
+}
+
+fn build_empty_state() -> gtk::Box {
+    let container = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .vexpand(true)
+        .hexpand(true)
+        .build();
+
+    let drop_zone = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(12)
+        .halign(gtk::Align::Center)
+        .valign(gtk::Align::Center)
+        .vexpand(true)
+        .margin_top(48)
+        .margin_bottom(48)
+        .margin_start(48)
+        .margin_end(48)
+        .build();
+    drop_zone.add_css_class("card");
+
+    let inner = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(12)
+        .margin_top(48)
+        .margin_bottom(48)
+        .margin_start(64)
+        .margin_end(64)
+        .halign(gtk::Align::Center)
+        .build();
+
+    let icon = gtk::Image::builder()
+        .icon_name("folder-pictures-symbolic")
+        .pixel_size(64)
+        .css_classes(["dim-label"])
+        .build();
+
+    let title = gtk::Label::builder()
+        .label("Drop images here")
+        .css_classes(["title-2"])
+        .build();
+
+    let subtitle = gtk::Label::builder()
+        .label("or click Browse to select files")
+        .css_classes(["dim-label"])
+        .build();
+
+    let browse_button = gtk::Button::builder()
+        .label("Browse Files")
+        .tooltip_text("Add image files (Ctrl+O)")
+        .halign(gtk::Align::Center)
+        .build();
+    browse_button.add_css_class("suggested-action");
+    browse_button.add_css_class("pill");
+
+    inner.append(&icon);
+    inner.append(&title);
+    inner.append(&subtitle);
+    inner.append(&browse_button);
+    drop_zone.append(&inner);
+
+    container.append(&drop_zone);
+    container
+}
+
+fn build_loaded_state() -> gtk::Box {
+    let container = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(0)
+        .build();
+
+    // Toolbar
+    let toolbar = gtk::Box::builder()
+        .orientation(gtk::Orientation::Horizontal)
+        .spacing(8)
+        .margin_start(12)
+        .margin_end(12)
+        .margin_top(8)
+        .margin_bottom(8)
+        .build();
+
+    let count_label = gtk::Label::builder()
+        .label("0 images (0 B)")
+        .hexpand(true)
+        .halign(gtk::Align::Start)
+        .css_classes(["heading"])
+        .build();
+
+    let add_button = gtk::Button::builder()
+        .icon_name("list-add-symbolic")
+        .tooltip_text("Add more images")
+        .build();
+    add_button.add_css_class("flat");
+
+    let select_all_button = gtk::Button::builder()
+        .label("Select All")
+        .tooltip_text("Select all images (Ctrl+A)")
+        .build();
+    select_all_button.add_css_class("flat");
+
+    toolbar.append(&count_label);
+    toolbar.append(&add_button);
+    toolbar.append(&select_all_button);
+
+    let separator = gtk::Separator::new(gtk::Orientation::Horizontal);
+
+    // Thumbnail grid placeholder
+    let grid_placeholder = adw::StatusPage::builder()
+        .title("Images will appear here")
+        .icon_name("image-x-generic-symbolic")
+        .vexpand(true)
+        .build();
+
+    container.append(&toolbar);
+    container.append(&separator);
+    container.append(&grid_placeholder);
+
+    container
+}