Expose dynamicTilingEnabled (default true) on MobileShellSettings,
stored under the General group of plasmamobilerc and re-emitted by
the existing config watcher. shift-tiling extends its activation
guard with this flag and clears the BSP layout when it goes false,
so users can fall back to KWin native quick-tile at will.
Add a quick-settings tile that surfaces the toggle. available is
gated on convergenceModeEnabled and !gamingModeEnabled, so the tile
is hidden on the phone form factor and during gaming sessions.
