Added two-click combat movement and clearer controls

I changed combat movement to use two clicks. The first click previews the route; the second confirms the destination and sends the selected survivor along it.

Confirmation works anywhere within the selected square, rather than requiring the exact same pixel. Right-click or Escape cancels the preview before time units are spent.

“Preview a combat route before committing, or cancel it without spending time units.”

Free movement keeps its own controls: another ground click changes course, Shift-click runs, and holding the right mouse button lets a stationary survivor face the cursor.

I also made refused moves explain their cause and corrected target picking over enemy silhouettes. The aim is to make the cursor and route preview match the action that will actually happen.