loadPackage + setPath can produce an invalid package if the shell
package is missing. Guard with isValid() to avoid passing a bad
package to setKPackage. Add the QML_SINGLETON factory that the
QML engine requires for proper singleton instantiation.
AppletHost: setPreloadFullRepresentation(true) does not guarantee
fullRepresentationItem() is non-null on return — the applet loads
asynchronously. Wire a single-shot connection to
fullRepresentationItemChanged to emit appletReady() when the item
arrives.
TaskWidget: operationDescription() can return null for an unknown
operation name; bail out rather than dereferencing it.
Long-pressing a mapped quick-settings tile in convergence
mode opens a floating popup with the Plasma applet UI
instead of launching System Settings. Unmapped tiles still
open Settings.
AppletHost creates a standalone Corona to host applets
outside the shell containment tree.
