Add GTK app shell with wizard navigation, step indicator, and actions

7-step wizard flow (Workflow, Images, Resize, Convert, Compress,
Metadata, Output) with AdwNavigationView, step indicator dots,
Back/Next buttons, keyboard shortcuts (Alt+arrows, Alt+1-9),
and hamburger menu with Settings and History placeholders.

pixstrip-gtk/src/step_indicator.rs

@@ -0,0 +1,126 @@
+use gtk::prelude::*;
+use std::cell::RefCell;
+
+#[derive(Clone)]
+pub struct StepIndicator {
+    container: gtk::Box,
+    dots: RefCell<Vec<StepDot>>,
+}
+
+#[derive(Clone)]
+struct StepDot {
+    button: gtk::Button,
+    icon: gtk::Image,
+    label: gtk::Label,
+}
+
+impl StepIndicator {
+    pub fn new(step_names: &[String]) -> Self {
+        let container = gtk::Box::builder()
+            .orientation(gtk::Orientation::Horizontal)
+            .halign(gtk::Align::Center)
+            .spacing(0)
+            .margin_top(8)
+            .margin_bottom(8)
+            .margin_start(12)
+            .margin_end(12)
+            .build();
+
+        let mut dots = Vec::new();
+
+        for (i, name) in step_names.iter().enumerate() {
+            if i > 0 {
+                // Connector line between dots
+                let line = gtk::Separator::builder()
+                    .orientation(gtk::Orientation::Horizontal)
+                    .hexpand(false)
+                    .valign(gtk::Align::Center)
+                    .build();
+                line.set_size_request(24, -1);
+                container.append(&line);
+            }
+
+            let dot_box = gtk::Box::builder()
+                .orientation(gtk::Orientation::Vertical)
+                .spacing(2)
+                .halign(gtk::Align::Center)
+                .build();
+
+            let icon = gtk::Image::builder()
+                .icon_name("radio-symbolic")
+                .pixel_size(16)
+                .build();
+
+            let button = gtk::Button::builder()
+                .child(&icon)
+                .has_frame(false)
+                .tooltip_text(format!("Step {}: {}", i + 1, name))
+                .sensitive(false)
+                .build();
+            button.add_css_class("circular");
+
+            let label = gtk::Label::builder()
+                .label(name)
+                .css_classes(["caption"])
+                .build();
+
+            dot_box.append(&button);
+            dot_box.append(&label);
+            container.append(&dot_box);
+
+            dots.push(StepDot {
+                button,
+                icon,
+                label,
+            });
+        }
+
+        // First step starts as current
+        if let Some(first) = dots.first() {
+            first.icon.set_icon_name(Some("radio-checked-symbolic"));
+            first.button.set_sensitive(true);
+            first.label.add_css_class("accent");
+        }
+
+        Self {
+            container,
+            dots: RefCell::new(dots),
+        }
+    }
+
+    pub fn set_current(&self, index: usize) {
+        let dots = self.dots.borrow();
+        for (i, dot) in dots.iter().enumerate() {
+            if i == index {
+                dot.icon.set_icon_name(Some("radio-checked-symbolic"));
+                dot.button.set_sensitive(true);
+                dot.label.add_css_class("accent");
+            } else if dot.icon.icon_name().as_deref() != Some("emblem-ok-symbolic") {
+                dot.icon.set_icon_name(Some("radio-symbolic"));
+                dot.label.remove_css_class("accent");
+            }
+        }
+    }
+
+    pub fn set_completed(&self, index: usize) {
+        let dots = self.dots.borrow();
+        if let Some(dot) = dots.get(index) {
+            dot.icon.set_icon_name(Some("emblem-ok-symbolic"));
+            dot.button.set_sensitive(true);
+            dot.label.remove_css_class("accent");
+        }
+    }
+
+    pub fn widget(&self) -> &gtk::Box {
+        &self.container
+    }
+}
+
+// Allow appending the step indicator to containers
+impl std::ops::Deref for StepIndicator {
+    type Target = gtk::Box;
+
+    fn deref(&self) -> &Self::Target {
+        &self.container
+    }
+}