Add game "Fox and Geese"

### Game Proposal: Fox and Geese

### Game Overview

Fox and Geese is a classic asymmetric, two-player, zero-sum, perfect-information medieval board game (originating in Northern Europe) played on a cross-shaped board.

* **Player 0 (The Fox):** Moves or jumps over adjacent Geese into empty spaces to capture them. The Fox wins if it captures enough Geese so that they can no longer immobilize the Fox.
* **Player 1 (The Geese):** Geese move to adjacent empty spaces to surround and trap the Fox. Geese win if the Fox has no legal moves remaining.

### Scope

I will be focusing specifically on **Fox and Geese** as detailed in the section [Fox and geese](https://en.wikipedia.org/wiki/Fox_games#Fox_and_geese), with **one fox** and the three traditional goose counts: **13, 15, or 17**. Other variants listed in the broader article (such as *Fox and Hounds* or *Halatafl*) are out of scope for this initial implementation.

No files, tests, or entry points are named in the proposal. Start by locating existing board-game implementations and their tests, then use the stated one-fox variants with 13, 15, or 17 geese as the completion boundary.

Written by the indexing model from the issue text.