Add tray UI: main.qml + ShareItem.qml

PlasmoidItem with a system-tray icon (active when a share is mounted) and a
popup grouping shares per host. ExpandableListItem rows toggle mount/unmount
and open the mounted folder; empty-state placeholder links to config.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package/contents/code/nas.js

@@ -122,6 +122,16 @@ function unmountCmd(mountpoint) {
     return shCmd("exec pkexec " + HELPER + " unmount \"$1\"", [mountpoint]);
 }
 
+// Resolve the user's home directory.
+function homeCmd() {
+    return shCmd("printf %s \"$HOME\"", []);
+}
+
+// Open a path in the default file manager.
+function openCmd(path) {
+    return shCmd("exec xdg-open \"$1\"", [path]);
+}
+
 // Save a password to KWallet (used by the config page). kwallet-query reads the
 // secret from stdin; we feed it via printf from a positional param. The value
 // is in this process's argv for the brief write (unavoidable with a CLI-only