Fix 26 bugs, edge cases, and consistency issues from fifth audit pass

Critical: undo toast now trashes only batch output files (not entire dir),
JPEG scanline write errors propagated, selective metadata write result returned.

High: zero-dimension guards in ResizeConfig/fit_within, negative aspect ratio
rejection, FM integration toggle infinite recursion guard, saturating counter
arithmetic in executor.

Medium: PNG compression level passed to oxipng, pct mode updates job_config,
external file loading updates step indicator, CLI undo removes history entries,
watch config write failures reported, fast-copy path reads image dimensions for
rename templates, discovery excludes unprocessable formats (heic/svg/ico/jxl),
CLI warns on invalid algorithm/overwrite values, resolve_collision trailing dot
fix, generation guards on all preview threads to cancel stale results, default
DPI aligned to 0, watermark text width uses char count not byte length.

Low: binary path escaped in Nautilus extension, file dialog filter aligned with
discovery, reset_wizard clears preset_mode and output_dir.

pixstrip-gtk/src/steps/mod.rs

@@ -8,3 +8,33 @@ pub mod step_rename;
 pub mod step_resize;
 pub mod step_watermark;
 pub mod step_workflow;
+
+use gtk::prelude::*;
+
+/// Creates a list factory for ComboRow dropdowns where labels never truncate.
+/// The default GTK factory ellipsizes text, which cuts off long option names.
+pub fn full_text_list_factory() -> gtk::SignalListItemFactory {
+    let factory = gtk::SignalListItemFactory::new();
+    factory.connect_setup(|_, item| {
+        let item = item.downcast_ref::<gtk::ListItem>().unwrap();
+        let label = gtk::Label::builder()
+            .xalign(0.0)
+            .margin_start(8)
+            .margin_end(8)
+            .margin_top(8)
+            .margin_bottom(8)
+            .build();
+        item.set_child(Some(&label));
+    });
+    factory.connect_bind(|_, item| {
+        let item = item.downcast_ref::<gtk::ListItem>().unwrap();
+        if let Some(obj) = item.item() {
+            if let Some(string_obj) = obj.downcast_ref::<gtk::StringObject>() {
+                if let Some(label) = item.child().and_downcast_ref::<gtk::Label>() {
+                    label.set_label(&string_obj.string());
+                }
+            }
+        }
+    });
+    factory
+}