Add collapsible watch folders panel in main window

Toggle button in the header bar reveals a bottom panel showing active
watch folders with their linked presets and watching status. The add
button opens Settings for full watch folder configuration.

pixstrip-gtk/src/app.rs

@@ -456,10 +456,35 @@ fn build_ui(app: &adw::Application) {
     bottom_bar.append(&separator);
     bottom_bar.append(&bottom_box);
 
+    // Watch folders collapsible panel
+    let watch_revealer = gtk::Revealer::builder()
+        .transition_type(gtk::RevealerTransitionType::SlideUp)
+        .reveal_child(false)
+        .build();
+
+    let watch_panel = build_watch_folder_panel();
+    watch_revealer.set_child(Some(&watch_panel));
+
+    // Watch folder toggle button in header
+    let watch_button = gtk::ToggleButton::builder()
+        .icon_name("folder-visiting-symbolic")
+        .tooltip_text("Watch Folders")
+        .build();
+    watch_button.add_css_class("flat");
+    header.pack_start(&watch_button);
+
+    {
+        let revealer = watch_revealer.clone();
+        watch_button.connect_toggled(move |btn| {
+            revealer.set_reveal_child(btn.is_active());
+        });
+    }
+
     // Main content layout
     let content_box = gtk::Box::new(gtk::Orientation::Vertical, 0);
     content_box.append(step_indicator.widget());
     content_box.append(&nav_view);
+    content_box.append(&watch_revealer);
 
     // Queue side panel
     let (queue_panel, queue_list_box) = build_queue_panel(&app_state);
@@ -3048,6 +3073,112 @@ fn format_duration(ms: u64) -> String {
     }
 }
 
+fn build_watch_folder_panel() -> gtk::Box {
+    let panel = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(0)
+        .build();
+
+    panel.append(&gtk::Separator::new(gtk::Orientation::Horizontal));
+
+    let inner = gtk::Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .spacing(8)
+        .margin_top(8)
+        .margin_bottom(8)
+        .margin_start(12)
+        .margin_end(12)
+        .build();
+
+    let header_box = gtk::Box::builder()
+        .orientation(gtk::Orientation::Horizontal)
+        .spacing(8)
+        .build();
+
+    let header_label = gtk::Label::builder()
+        .label("Watch Folders")
+        .css_classes(["heading"])
+        .hexpand(true)
+        .halign(gtk::Align::Start)
+        .build();
+    header_box.append(&header_label);
+
+    // Quick add button
+    let add_btn = gtk::Button::builder()
+        .icon_name("list-add-symbolic")
+        .tooltip_text("Add watch folder")
+        .build();
+    add_btn.add_css_class("flat");
+    header_box.append(&add_btn);
+
+    inner.append(&header_box);
+
+    // List of active watch folders
+    let list_box = gtk::ListBox::builder()
+        .selection_mode(gtk::SelectionMode::None)
+        .css_classes(["boxed-list"])
+        .build();
+
+    let empty_label = gtk::Label::builder()
+        .label("No watch folders active. Add one in Settings or click +.")
+        .css_classes(["dim-label", "caption"])
+        .halign(gtk::Align::Center)
+        .wrap(true)
+        .margin_top(4)
+        .margin_bottom(4)
+        .build();
+
+    // Populate from config
+    let config_store = pixstrip_core::storage::ConfigStore::new();
+    let config = config_store.load().unwrap_or_default();
+    let has_folders = !config.watch_folders.is_empty();
+
+    for folder in &config.watch_folders {
+        if !folder.active {
+            continue;
+        }
+        let display_name = folder.path.file_name()
+            .and_then(|n| n.to_str())
+            .unwrap_or_else(|| folder.path.to_str().unwrap_or("Unknown"));
+
+        let row = adw::ActionRow::builder()
+            .title(display_name)
+            .subtitle(&folder.preset_name)
+            .build();
+        row.add_prefix(&gtk::Image::from_icon_name("folder-visiting-symbolic"));
+
+        // Status indicator
+        let status = gtk::Label::builder()
+            .label("Watching")
+            .css_classes(["caption", "accent"])
+            .valign(gtk::Align::Center)
+            .build();
+        row.add_suffix(&status);
+
+        list_box.append(&row);
+    }
+
+    empty_label.set_visible(!has_folders || config.watch_folders.iter().all(|f| !f.active));
+    list_box.set_visible(has_folders && config.watch_folders.iter().any(|f| f.active));
+
+    inner.append(&list_box);
+    inner.append(&empty_label);
+
+    // Wire add button to open Settings > Watch Folders
+    {
+        let inner_ref = inner.clone();
+        add_btn.connect_clicked(move |btn| {
+            if let Some(root) = btn.root() {
+                root.activate_action("win.show-settings", None).ok();
+            }
+            let _ = &inner_ref;
+        });
+    }
+
+    panel.append(&inner);
+    panel
+}
+
 fn build_queue_panel(_state: &AppState) -> (gtk::Box, gtk::ListBox) {
     let panel = gtk::Box::builder()
         .orientation(gtk::Orientation::Vertical)