Add EXIF auto-orient and aspect ratio lock toggle

- Implement auto_orient_from_exif() that reads EXIF Orientation tag
  and applies the correct rotation/flip for all 8 EXIF orientations
- Add aspect ratio lock toggle to resize step Width/Height mode
- When lock is active, changing width auto-calculates height from
  the first loaded image's aspect ratio, and vice versa
- Uses recursive update guard (Cell<bool>) to prevent infinite loops

pixstrip-gtk/src/steps/step_resize.rs

@@ -2,6 +2,15 @@ use adw::prelude::*;
 use gtk::glib;
 use crate::app::AppState;
 
+/// Get the aspect ratio (width/height) of the first loaded image.
+/// Returns 0.0 if no images are loaded or the image can't be read.
+fn get_first_image_aspect(files: &[std::path::PathBuf]) -> f64 {
+    let Some(first) = files.first() else { return 0.0 };
+    let Ok((w, h)) = image::image_dimensions(first) else { return 0.0 };
+    if h == 0 { return 0.0; }
+    w as f64 / h as f64
+}
+
 pub fn build_resize_page(state: &AppState) -> adw::NavigationPage {
     let scrolled = gtk::ScrolledWindow::builder()
         .hscrollbar_policy(gtk::PolicyType::Never)
@@ -61,6 +70,13 @@ pub fn build_resize_page(state: &AppState) -> adw::NavigationPage {
         .adjustment(&gtk::Adjustment::new(cfg.resize_width as f64, 0.0, 10000.0, 1.0, 100.0, 0.0))
         .build();
 
+    let lock_row = adw::SwitchRow::builder()
+        .title("Lock Aspect Ratio")
+        .subtitle("Changing one dimension auto-calculates the other")
+        .active(true)
+        .build();
+    lock_row.add_prefix(&gtk::Image::from_icon_name("changes-prevent-symbolic"));
+
     let height_row = adw::SpinRow::builder()
         .title("Height")
         .subtitle("Target height in pixels (0 = auto from aspect ratio)")
@@ -68,6 +84,7 @@ pub fn build_resize_page(state: &AppState) -> adw::NavigationPage {
         .build();
 
     wh_group.add(&width_row);
+    wh_group.add(&lock_row);
     wh_group.add(&height_row);
     wh_box.append(&wh_group);
 
@@ -524,28 +541,70 @@ pub fn build_resize_page(state: &AppState) -> adw::NavigationPage {
             jc.borrow_mut().resize_enabled = row.is_active();
         });
     }
+    // Shared flag to prevent recursive updates from aspect ratio lock
+    let updating_lock = std::rc::Rc::new(std::cell::Cell::new(false));
     {
         let jc = state.job_config.clone();
         let pw = preview_width.clone();
+        let ph = preview_height.clone();
         let draw = drawing.clone();
         let rt = render_thumb.clone();
+        let lock = lock_row.clone();
+        let hr = height_row.clone();
+        let files = state.loaded_files.clone();
+        let upd = updating_lock.clone();
         width_row.connect_value_notify(move |row| {
+            if upd.get() { return; }
             let val = row.value() as u32;
             jc.borrow_mut().resize_width = val;
             *pw.borrow_mut() = val;
+
+            // Auto-calculate height if lock is active
+            if lock.is_active() && val > 0 {
+                let aspect = get_first_image_aspect(&files.borrow());
+                if aspect > 0.0 {
+                    let new_h = (val as f64 / aspect).round() as u32;
+                    upd.set(true);
+                    hr.set_value(new_h as f64);
+                    jc.borrow_mut().resize_height = new_h;
+                    *ph.borrow_mut() = new_h;
+                    upd.set(false);
+                }
+            }
+
             draw.queue_draw();
             rt();
         });
     }
     {
         let jc = state.job_config.clone();
+        let pw = preview_width.clone();
         let ph = preview_height.clone();
         let draw = drawing.clone();
         let rt = render_thumb.clone();
+        let lock = lock_row.clone();
+        let wr = width_row.clone();
+        let files = state.loaded_files.clone();
+        let upd = updating_lock.clone();
         height_row.connect_value_notify(move |row| {
+            if upd.get() { return; }
             let val = row.value() as u32;
             jc.borrow_mut().resize_height = val;
             *ph.borrow_mut() = val;
+
+            // Auto-calculate width if lock is active
+            if lock.is_active() && val > 0 {
+                let aspect = get_first_image_aspect(&files.borrow());
+                if aspect > 0.0 {
+                    let new_w = (val as f64 * aspect).round() as u32;
+                    upd.set(true);
+                    wr.set_value(new_w as f64);
+                    jc.borrow_mut().resize_width = new_w;
+                    *pw.borrow_mut() = new_w;
+                    upd.set(false);
+                }
+            }
+
             draw.queue_draw();
             rt();
         });