Replace bar-settings with unified settings plugin

Consolidates bar-settings into a single 'settings' plugin with sidebar
categories: Defaults, Style, Bar, System, Plugins. Updates supporting
commands (omarchy-launch-settings, omarchy-style-corners-quickshell,
omarchy-theme-list-with-previews, omarchy-hyprland-monitor-scaling-set)
and refreshes sidebar glyphs to Nerd Font icons.

bin/omarchy-theme-list-with-previews

@@ -0,0 +1,26 @@
+#!/bin/bash
+
+# omarchy:summary=List themes with preview image paths (tab-separated: name\tslug\tpreview)
+# omarchy:hidden=true
+
+OMARCHY_PATH=${OMARCHY_PATH:-$HOME/.local/share/omarchy}
+
+omarchy-theme-list 2>/dev/null | while IFS= read -r name; do
+  [[ -n $name ]] || continue
+  slug=$(printf '%s' "$name" | tr '[:upper:]' '[:lower:]' | tr ' ' '-')
+  preview=""
+  for base in "$HOME/.config/omarchy/themes" "$OMARCHY_PATH/themes"; do
+    [[ -d $base/$slug ]] || continue
+    for ext in png jpg jpeg webp; do
+      if [[ -f $base/$slug/preview.$ext ]]; then
+        preview="$base/$slug/preview.$ext"
+        break 2
+      fi
+    done
+    if [[ -z $preview && -d $base/$slug/backgrounds ]]; then
+      preview=$(find -L "$base/$slug/backgrounds" -maxdepth 1 -type f \( -iname '*.jpg' -o -iname '*.jpeg' -o -iname '*.png' -o -iname '*.webp' \) 2>/dev/null | sort | head -n1)
+      [[ -n $preview ]] && break
+    fi
+  done
+  printf '%s\t%s\t%s\n' "$name" "$slug" "$preview"
+done