Add arena gifs

Author: john-b-yang

pages/arenas/battlesnake.md

@@ -1,5 +1,6 @@
 title: Battlesnake
 logo: /static/images/arenas/battlesnake.png
+preview: /static/images/arenas/battlesnake.gif
 description: Snake AIs compete to survive and grow in a grid
 date-added: 2025-11-04
 players: 2+

pages/arenas/corewar.md

@@ -1,5 +1,7 @@
 title: Core War
 logo: /static/images/arenas/corewar.png
+preview: /static/images/arenas/corewar.gif
+preview_width: 70
 description: Redcode warriors battle to control a virtual computer
 date-added: 2025-11-04
 players: 2+

pages/arenas/halite.md

@@ -1,5 +1,7 @@
 title: Halite
 logo: /static/images/arenas/halite.png
+preview: /static/images/arenas/halite.gif
+preview_width: 70
 description: Distribute resources wisely to conquer territory
 date-added: 2025-11-04
 players: 2+

pages/arenas/poker.md

@@ -1,5 +1,7 @@
 title: Poker
 logo: /static/images/arenas/poker.png
+preview: /static/images/arenas/poker.gif
+preview_width: 70
 description: No Limit Texas Hold'em with 2+ players
 date-added: 2025-11-04
 players: 2+

pages/arenas/robocode.md

@@ -1,5 +1,7 @@
 title: RoboCode
 logo: /static/images/arenas/robocode.png
+preview: /static/images/arenas/robocode.gif
+preview_width: 70
 description: Tank combat - outlast and outgun opponents
 date-added: 2025-11-04
 players: 2+

pages/arenas/robotrumble.md

@@ -1,6 +1,6 @@
 title: RobotRumble
 logo: /static/images/arenas/robotrumble.png
-preview: /static/images/arenas/robotrumble_gif.gif
+preview: /static/images/arenas/robotrumble.gif
 description: Program swarms to overwhelm opponents
 date-added: 2025-11-04
 players: 2