Add ETA calculation, activity log, keyboard shortcuts, expand format options

- Processing: ETA calculated from elapsed time and progress, per-image log
  entries added to activity log with auto-scroll
- Keyboard shortcuts: Ctrl+Q quit, Ctrl+, settings, Ctrl+?/F1 shortcuts dialog
- Shortcuts dialog: AdwAlertDialog with all keyboard shortcuts listed
- Hamburger menu: added Keyboard Shortcuts entry
- Convert step: added AVIF, GIF, TIFF format options with descriptions
- Resize step: removed duplicate rotate/flip (now in Adjustments step),
  added missing social media presets (PeerTube, Friendica, Funkwhale,
  Instagram Portrait, Facebook Cover/Profile, LinkedIn Cover/Profile,
  TikTok, YouTube Channel Art, Threads, Twitter/X, 4K, etc.)

pixstrip-gtk/src/steps/step_convert.rs

@@ -33,6 +33,7 @@ pub fn build_convert_page(state: &AppState) -> adw::NavigationPage {
     // Format selection
     let format_group = adw::PreferencesGroup::builder()
         .title("Output Format")
+        .description("Choose the format all images will be converted to")
         .build();
 
     let format_row = adw::ComboRow::builder()
@@ -41,9 +42,12 @@ pub fn build_convert_page(state: &AppState) -> adw::NavigationPage {
         .build();
     let format_model = gtk::StringList::new(&[
         "Keep Original",
-        "JPEG - universal, lossy",
-        "PNG - lossless, graphics",
+        "JPEG - universal, lossy, photos",
+        "PNG - lossless, graphics, transparency",
         "WebP - modern, excellent compression",
+        "AVIF - next-gen, best compression",
+        "GIF - animations, limited colors",
+        "TIFF - archival, lossless, large files",
     ]);
     format_row.set_model(Some(&format_model));
 
@@ -53,10 +57,24 @@ pub fn build_convert_page(state: &AppState) -> adw::NavigationPage {
         Some(ImageFormat::Jpeg) => 1,
         Some(ImageFormat::Png) => 2,
         Some(ImageFormat::WebP) => 3,
-        _ => 0,
+        Some(ImageFormat::Avif) => 4,
+        Some(ImageFormat::Gif) => 5,
+        Some(ImageFormat::Tiff) => 6,
     });
 
     format_group.add(&format_row);
+
+    // Format info label
+    let info_label = gtk::Label::builder()
+        .label(format_info(cfg.convert_format))
+        .css_classes(["dim-label", "caption"])
+        .halign(gtk::Align::Start)
+        .wrap(true)
+        .margin_top(4)
+        .margin_bottom(8)
+        .margin_start(12)
+        .build();
+    format_group.add(&info_label);
     content.append(&format_group);
 
     drop(cfg);
@@ -70,14 +88,19 @@ pub fn build_convert_page(state: &AppState) -> adw::NavigationPage {
     }
     {
         let jc = state.job_config.clone();
+        let label = info_label;
         format_row.connect_selected_notify(move |row| {
             let mut c = jc.borrow_mut();
             c.convert_format = match row.selected() {
                 1 => Some(ImageFormat::Jpeg),
                 2 => Some(ImageFormat::Png),
                 3 => Some(ImageFormat::WebP),
+                4 => Some(ImageFormat::Avif),
+                5 => Some(ImageFormat::Gif),
+                6 => Some(ImageFormat::Tiff),
                 _ => None,
             };
+            label.set_label(&format_info(c.convert_format));
         });
     }
 
@@ -94,3 +117,15 @@ pub fn build_convert_page(state: &AppState) -> adw::NavigationPage {
         .child(&clamp)
         .build()
 }
+
+fn format_info(format: Option<ImageFormat>) -> String {
+    match format {
+        None => "Images will keep their original format.".into(),
+        Some(ImageFormat::Jpeg) => "JPEG: Best for photographs. Lossy compression, no transparency. Universally supported.".into(),
+        Some(ImageFormat::Png) => "PNG: Best for graphics, screenshots, logos. Lossless, supports transparency. Larger files.".into(),
+        Some(ImageFormat::WebP) => "WebP: Modern format with excellent lossy and lossless compression. Supports transparency and animation. Widely supported in browsers.".into(),
+        Some(ImageFormat::Avif) => "AVIF: Next-generation format based on AV1. Best compression ratios, supports transparency and HDR. Slower to encode, growing browser support.".into(),
+        Some(ImageFormat::Gif) => "GIF: Limited to 256 colors. Supports animation and transparency. Best for simple graphics and short animations.".into(),
+        Some(ImageFormat::Tiff) => "TIFF: Professional archival format. Lossless, supports layers and metadata. Very large files. Not suitable for web use.".into(),
+    }
+}