Improved AI, *another* UI reorg

Only minimal gameplay changes this time; I'm deploying now because it might be a while until the next once since I'm preparing to upgrade from Godot 3.5 to 4.0.

Gameplay changes:

• Added PC downloadable version which should have better performance than the in-browser version.
• Improved AI; better deciding who to target, pathfinding to them, usage of whatever gear is available.
• Overwatching requires line of sight.
• Nelson skirmisher works on killshots.
• Knockback works on killshots.
• Rams don't trigger berserker aggression.
• Mines are not selectable/attackable.

UI/UX changes:

• Replaced the corner portraits that took up like a sixth of the screen with this crosshair on the focused unit.

• Added outline to text on the map to improve contrast and readability.
• Bounce the mech whose turn it is while not focused on them.
• New dialogue portrait layout since we can't use the corner portraits anymore.
• New tooltip system so they'll never get cut off by the edge of the screen.
• Add Striker, Defender, etc roles to the squad chooser.
• Boost confirm window uses smaller, more minimal box.
• Broke undo move function into its own button instead of tying it to the cancel system.
• Add a little warning exclamation point to enemies that will overwatch you on a move. Will add an explicit confirm box someday.
• Add movement path arrows.
• Changed color of system buttons to distinguish them from tech attack buttons.