Reduce Settings page and config reload overhead

Mount nearby shortcut and theme rows, preserve gallery keyboard navigation, reset page scrolling, and reuse native themes during palette transitions. Prepare and deduplicate live config reloads on a worker and apply only changed runtime sections.

Align pointer focus and overview selection on overlapping outputs, add regression coverage, and clean up workspace Clippy warnings.

shell/ferese-settings/src/theme_controls.rs

@@ -156,15 +156,9 @@ impl App {
             .into()
     }
 
-    pub(super) fn theme_gallery(
-        &self,
-        appearance: Option<ferese_config::theme::Appearance>,
-    ) -> Element<'static, Message> {
+    pub(super) fn theme_gallery(&self, appearance: Option<ferese_config::theme::Appearance>) -> Element<'_, Message> {
         use ferese_config::theme::Appearance::{Dark, Light};
-        let palette = visuals::Palette::from_resolved(&self.resolved.presented);
-        let selected_id = visuals::family_selection(&self.draft, appearance);
-        let choices = self.resolved.families.clone();
-        let ids: Vec<_> = choices.iter().map(|family| family.id.clone()).collect();
+        let choices = &self.resolved.families;
         let mut heading = row([]).align_y(Alignment::Center).spacing(6).push(
             self.label(
                 match appearance {
@@ -192,38 +186,30 @@ impl App {
             ));
         }
         let mut gallery = column([]).spacing(6).push(heading);
-        for (chunk, families) in choices.chunks(3).enumerate() {
-            let mut tiles = row([]).spacing(6);
-            for (offset, family) in families.iter().enumerate() {
-                let selected = family.id == selected_id;
-                let index = chunk * 3 + offset;
-                let id = family.id.clone();
-                let active = selected
-                    .then_some(self.resolved.theme.appearance)
-                    .filter(|a| appearance.is_none_or(|variant| variant == *a));
-                let ids = ids.clone();
-                let tile_id = gallery_id(&id, appearance);
-                tiles = tiles.push(gallery::tile(
-                    family,
-                    gallery::TileOptions {
-                        variant: appearance,
-                        active,
-                        selected,
-                        palette,
-                        font: self.font,
-                        id: tile_id,
-                    },
-                    Message::Family(id, appearance),
-                    move |key| {
-                        gallery::neighbor(index, ids.len(), key)
-                            .map(|index| Message::Family(ids[index].clone(), appearance))
-                    },
-                ));
-            }
-            for _ in families.len()..3 {
-                tiles = tiles.push(widget::Space::new().width(Length::Fill));
-            }
-            gallery = gallery.push(tiles);
+        let list = crate::navigation::gallery_list(appearance);
+        for chunk in 0..choices.len().div_ceil(3) {
+            let content = widget::responsive(move |size| {
+                // Three previews: 200:126 image, caption, and tile padding.
+                let height = ((size.width - 12.) / 3. - 16.).max(0.) * 126. / 200. + 34.;
+                let content: Element<'_, Message> = if self.visible_rows.contains(&(list, chunk)) {
+                    // Rebuild only mounted rows; responsive owns their actual layout width.
+                    self.theme_gallery_row(chunk, appearance)
+                } else {
+                    widget::Space::new().height(height).width(Length::Fill).into()
+                };
+                cosmic::iced::widget::sensor(
+                    container(content)
+                        .height(height)
+                        .id(crate::navigation::gallery_row_id(list, chunk)),
+                )
+                .key((list, chunk))
+                .anticipate(200)
+                .on_show(move |_| Message::RowVisibility(list, chunk, true))
+                .on_hide(Message::RowVisibility(list, chunk, false))
+                .into()
+            })
+            .height(Length::Shrink);
+            gallery = gallery.push(content);
         }
         gallery::group(
             container(gallery).width(Length::Fill),
@@ -235,6 +221,49 @@ impl App {
             },
         )
     }
+
+    fn theme_gallery_row(
+        &self,
+        chunk: usize,
+        appearance: Option<ferese_config::theme::Appearance>,
+    ) -> Element<'static, Message> {
+        let palette = visuals::Palette::from_resolved(&self.resolved.presented);
+        let selected_id = visuals::family_selection(&self.draft, appearance);
+        let families = &self.resolved.families[chunk * 3..self.resolved.families.len().min(chunk * 3 + 3)];
+        let ids = &self.family_ids;
+        let mut tiles = row([]).spacing(6);
+        for (offset, family) in families.iter().enumerate() {
+            let selected = family.id == selected_id;
+            let index = chunk * 3 + offset;
+            let id = family.id.clone();
+            let active = selected
+                .then_some(self.resolved.theme.appearance)
+                .filter(|a| appearance.is_none_or(|variant| variant == *a));
+            let tile_id = gallery_id(&id, appearance);
+            let ids = ids.clone();
+            tiles = tiles.push(gallery::tile(
+                family,
+                gallery::TileOptions {
+                    variant: appearance,
+                    active,
+                    selected,
+                    palette,
+                    font: self.font,
+                    id: tile_id,
+                },
+                Message::Family(id, appearance),
+                move |key| {
+                    gallery::neighbor(index, ids.len(), key)
+                        .map(|index| Message::Family(ids[index].clone(), appearance))
+                },
+            ));
+        }
+        for _ in families.len()..3 {
+            tiles = tiles.push(widget::Space::new().width(Length::Fill));
+        }
+
+        tiles.into()
+    }
 }
 
 pub(super) fn gallery_id(