Improve UX, add popover tour, metadata, and hicolor icons

- Redesign tutorial tour from modal dialogs to popovers pointing at actual UI elements
- Add beginner-friendly improvements: help buttons, tooltips, welcome wizard enhancements
- Add AppStream metainfo with screenshots, branding, categories, keywords, provides
- Update desktop file with GTK category and SingleMainWindow
- Add hicolor icon theme with all sizes (16-512px)
- Fix debounce SourceId panic in rename step
- Various step UI improvements and bug fixes

pixstrip-gtk/src/steps/step_adjustments.rs

@@ -25,6 +25,7 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         .title("Enable Adjustments")
         .subtitle("Rotate, flip, brightness, contrast, effects")
         .active(cfg.adjustments_enabled)
+        .tooltip_text("Toggle image adjustments on or off")
         .build();
     enable_group.add(&enable_row);
     outer.append(&enable_group);
@@ -37,6 +38,10 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         .vexpand(true)
         .build();
     preview_picture.set_can_target(true);
+    preview_picture.set_focusable(true);
+    preview_picture.update_property(&[
+        gtk::accessible::Property::Label("Adjustments preview - press Space to cycle images"),
+    ]);
 
     let info_label = gtk::Label::builder()
         .label("No images loaded")
@@ -78,6 +83,7 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         .title("Rotate")
         .subtitle("Rotation applied to all images")
         .use_subtitle(true)
+        .tooltip_text("Rotate all images by a fixed angle or auto-orient from EXIF")
         .build();
     rotate_row.set_model(Some(&gtk::StringList::new(&[
         "None",
@@ -93,6 +99,7 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         .title("Flip")
         .subtitle("Mirror the image")
         .use_subtitle(true)
+        .tooltip_text("Mirror images horizontally or vertically")
         .build();
     flip_row.set_model(Some(&gtk::StringList::new(&["None", "Horizontal", "Vertical"])));
     flip_row.set_list_factory(Some(&super::full_text_list_factory()));
@@ -130,6 +137,9 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
             .tooltip_text("Reset to 0")
             .has_frame(false)
             .build();
+        reset_btn.update_property(&[
+            gtk::accessible::Property::Label(&format!("Reset {} to 0", title)),
+        ]);
         reset_btn.set_sensitive(value != 0);
 
         row.add_suffix(&scale);
@@ -204,6 +214,7 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         .title("Crop to Aspect Ratio")
         .subtitle("Crop from center to a specific ratio")
         .use_subtitle(true)
+        .tooltip_text("Crop from center to a specific aspect ratio")
         .build();
     crop_row.set_model(Some(&gtk::StringList::new(&[
         "None",
@@ -222,12 +233,14 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         .title("Trim Whitespace")
         .subtitle("Remove uniform borders around the image")
         .active(cfg.trim_whitespace)
+        .tooltip_text("Detect and remove uniform borders around the image")
         .build();
 
     let padding_row = adw::SpinRow::builder()
         .title("Canvas Padding")
         .subtitle("Add uniform padding (pixels)")
         .adjustment(&gtk::Adjustment::new(cfg.canvas_padding as f64, 0.0, 500.0, 1.0, 10.0, 0.0))
+        .tooltip_text("Add a white border around each image in pixels")
         .build();
 
     crop_group.add(&crop_row);
@@ -506,6 +519,27 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         preview_picture.add_controller(click);
     }
 
+    // Keyboard support for preview cycling (Space/Enter)
+    {
+        let key = gtk::EventControllerKey::new();
+        let pidx = preview_index.clone();
+        let files = state.loaded_files.clone();
+        let up = update_preview.clone();
+        key.connect_key_pressed(move |_, keyval, _, _| {
+            if keyval == gtk::gdk::Key::space || keyval == gtk::gdk::Key::Return {
+                let loaded = files.borrow();
+                if loaded.len() > 1 {
+                    let next = (pidx.get() + 1) % loaded.len();
+                    pidx.set(next);
+                    up();
+                }
+                return glib::Propagation::Stop;
+            }
+            glib::Propagation::Proceed
+        });
+        preview_picture.add_controller(key);
+    }
+
     // === Wire signals ===
 
     {
@@ -694,12 +728,16 @@ pub fn build_adjustments_page(state: &AppState) -> adw::NavigationPage {
         .child(&outer)
         .build();
 
-    // Refresh preview and sensitivity when navigating to this page
+    // Sync enable toggle, refresh preview and sensitivity when navigating to this page
     {
         let up = update_preview.clone();
         let lf = state.loaded_files.clone();
         let ctrl = controls.clone();
+        let jc = state.job_config.clone();
+        let er = enable_row.clone();
         page.connect_map(move |_| {
+            let enabled = jc.borrow().adjustments_enabled;
+            er.set_active(enabled);
             ctrl.set_sensitive(!lf.borrow().is_empty());
             up();
         });