It is late here now, but I can list a few quick examples:
Ambush! is my favorite, using paragraphs and look-up tables to drive game events, including the exact movement path (hex by hex) of every enemy unit. No enemy action is left to the player to decide (and this is made explicit in the rules). The first sequel Battle Hymn was also like that, but the second one, Open Fire, did not specify exact movement paths for enemy units (the player has to carry out instructions such as "move best possible path towards
" which is not what I would include in 100 % solitaire.
Two Strategy & Tactics games from the 90's, Red Beach One: Tarawa and Saipan use the same system. There are not even enemy units on the map, only fortifications (although some may briefly appear to counterattack, but are removed after resolving that). Obviously never a need for the player to make moves for the enemy, since there is nothing to move.
Two newer examples:
Fields of Fire (the system even makes some decisions for friendly units) and D-Day on Omaha Beach. The former use an abstract map with only a few areas, so enemy movement and orders can be specific without much difficulty. The latter has a hex map, but enemy units only move from one strongpoint to another (following arrows printed on the map), so they are in fact moving on a very simple point-2-point-map (unlike friendly units that move freely from hex to hex).
Many of the solitaire games from Minden Games. I only played 3, but read about a few more, and at least all those are 100 % solitaire. Typically enemy units do not move at all, or only rarely (triggered by random events).
I think it is easier to list the solitaire boardgames that are not 100 % solitaire, but leave some decisions to the player. Can only think of Open Fire.
My hypothesis was that it is very difficult to construct such a system when you have no grid, since I can't think of ways to give exact movement instructions. But it looks like THW mentioend above do come pretty close, and it was interesting to see that (I'm sure there are a few other examples). But that trick in the D-Day game ought to work well in a free movement game too, if the situation is suitable for only allowing enemies to move from cover to cover, and you can set up some tables to decide when units run for the next cover. Maybe someone did something like that?
Personally I'm thinking of stealing some ideas from the boardgames to use in a grid-based solitaire wargame. But no very concrete plans yet.