refactor: group stow packages into common, mac and kde

Split the packages by platform so each app stays an opt-in Stow package
under common/, mac/ or kde/. KDE gets its own Fastfetch, Helium and
Spectacle packages, and darwin-breeze becomes kde/theme. The READMEs
document stowing a whole group as well as individual packages.

kde/tray-icons/.local/share/ngosen-breeze-icons/apply.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+# Copy the Breeze-style icons over Ngó Sen's monochrome tray icons.
+# Runs as root; the pacman hook re-runs it after every fcitx5-ngosen install/upgrade.
+set -euo pipefail
+here=$(cd "$(dirname "$0")" && pwd)
+ROOT=${ROOT:-}   # for dry-run testing only
+
+# Ngó Sen points at hicolor, but Plasma looks the icon up by name in breeze/breeze-dark
+dirs=(usr/share/icons/hicolor/scalable/{apps,status}
+      usr/share/icons/breeze{,-dark}/status/{22,24})
+mtree=$(zcat "$ROOT"/var/lib/pacman/local/fcitx5-ngosen-*/mtree 2>/dev/null || true)
+
+for d in "${dirs[@]}"; do
+  for f in "$here"/icons/*.svg; do
+    n=$(basename "$f"); t=$ROOT/$d/$n
+    [[ -f $t ]] || continue
+    # Still the file the package installed: keep it as the original for restore.sh
+    sum=$(grep -F "./$d/$n " <<<"$mtree" | grep -o 'sha256digest=[0-9a-f]*' | cut -d= -f2 || true)
+    if [[ -n $sum && $(sha256sum <"$t" | cut -d' ' -f1) == "$sum" ]]; then
+      install -Dm644 "$t" "$here/orig/$d/$n"
+    fi
+    install -m644 "$f" "$t"
+  done
+done