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_workflow.rs

@@ -0,0 +1,179 @@
+use adw::prelude::*;
+use pixstrip_core::preset::Preset;
+
+pub fn build_workflow_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();
+
+    // Built-in presets section
+    let builtin_group = adw::PreferencesGroup::builder()
+        .title("Built-in Workflows")
+        .description("Select a preset to get started quickly")
+        .build();
+
+    let builtin_flow = gtk::FlowBox::builder()
+        .selection_mode(gtk::SelectionMode::Single)
+        .max_children_per_line(4)
+        .min_children_per_line(2)
+        .row_spacing(8)
+        .column_spacing(8)
+        .homogeneous(true)
+        .build();
+
+    for preset in Preset::all_builtins() {
+        let card = build_preset_card(&preset);
+        builtin_flow.append(&card);
+    }
+
+    builtin_group.add(&builtin_flow);
+    content.append(&builtin_group);
+
+    // Custom workflow section
+    let custom_group = adw::PreferencesGroup::builder()
+        .title("Custom Workflow")
+        .description("Choose which operations to include")
+        .build();
+
+    let custom_card = build_custom_card();
+    let custom_flow = gtk::FlowBox::builder()
+        .selection_mode(gtk::SelectionMode::None)
+        .max_children_per_line(4)
+        .min_children_per_line(2)
+        .build();
+    custom_flow.append(&custom_card);
+    custom_group.add(&custom_flow);
+    content.append(&custom_group);
+
+    // User presets section (initially empty)
+    let user_group = adw::PreferencesGroup::builder()
+        .title("Your Presets")
+        .description("Import or save your own workflows")
+        .build();
+
+    let import_button = gtk::Button::builder()
+        .label("Import Preset")
+        .icon_name("document-open-symbolic")
+        .build();
+    import_button.add_css_class("flat");
+    user_group.add(&import_button);
+    content.append(&user_group);
+
+    scrolled.set_child(Some(&content));
+
+    let clamp = adw::Clamp::builder()
+        .maximum_size(800)
+        .child(&scrolled)
+        .build();
+
+    adw::NavigationPage::builder()
+        .title("Choose a Workflow")
+        .tag("step-workflow")
+        .child(&clamp)
+        .build()
+}
+
+fn build_preset_card(preset: &Preset) -> gtk::Box {
+    let card = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(8)
+        .halign(gtk::Align::Center)
+        .valign(gtk::Align::Start)
+        .build();
+    card.add_css_class("card");
+    card.set_size_request(180, 120);
+
+    let inner = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(4)
+        .margin_top(16)
+        .margin_bottom(16)
+        .margin_start(12)
+        .margin_end(12)
+        .halign(gtk::Align::Center)
+        .valign(gtk::Align::Center)
+        .vexpand(true)
+        .build();
+
+    let icon = gtk::Image::builder()
+        .icon_name(&preset.icon)
+        .pixel_size(32)
+        .build();
+
+    let name_label = gtk::Label::builder()
+        .label(&preset.name)
+        .css_classes(["heading"])
+        .build();
+
+    let desc_label = gtk::Label::builder()
+        .label(&preset.description)
+        .css_classes(["caption", "dim-label"])
+        .wrap(true)
+        .justify(gtk::Justification::Center)
+        .max_width_chars(20)
+        .build();
+
+    inner.append(&icon);
+    inner.append(&name_label);
+    inner.append(&desc_label);
+    card.append(&inner);
+
+    card
+}
+
+fn build_custom_card() -> gtk::Box {
+    let card = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(8)
+        .halign(gtk::Align::Center)
+        .valign(gtk::Align::Start)
+        .build();
+    card.add_css_class("card");
+    card.set_size_request(180, 120);
+
+    let inner = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(4)
+        .margin_top(16)
+        .margin_bottom(16)
+        .margin_start(12)
+        .margin_end(12)
+        .halign(gtk::Align::Center)
+        .valign(gtk::Align::Center)
+        .vexpand(true)
+        .build();
+
+    let icon = gtk::Image::builder()
+        .icon_name("applications-system-symbolic")
+        .pixel_size(32)
+        .build();
+
+    let name_label = gtk::Label::builder()
+        .label("Custom...")
+        .css_classes(["heading"])
+        .build();
+
+    let desc_label = gtk::Label::builder()
+        .label("Pick your own operations")
+        .css_classes(["caption", "dim-label"])
+        .wrap(true)
+        .justify(gtk::Justification::Center)
+        .build();
+
+    inner.append(&icon);
+    inner.append(&name_label);
+    inner.append(&desc_label);
+    card.append(&inner);
+
+    card
+}