feat: 15 Bitcoin-themed arenas (40 total)

bitcoin_mine, lightning_node, satoshis_garage, mempool, silk_road_ruins,
block_height_tower, hodl_cave, whale_pool, node_farm, genesis_block,
pizza_day_parlor, difficulty_adjustment, fifty_one_percent,
timechain_temple, nostr_relay_room. Each with unique theme colors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/game/FightScene.ts

@@ -75,6 +75,21 @@ const ARENA_THEMES: Record<string, { bg: string; ground: string; accent: string
   savanna: { bg: '#1a1808', ground: '#8a7830', accent: '#dd9922' },
   server_room: { bg: '#000a05', ground: '#0a1a10', accent: '#00ff88' },
   sports_arena: { bg: '#0a0a1a', ground: '#1a2a4a', accent: '#ff3333' },
+  bitcoin_mine: { bg: '#0a0808', ground: '#1a1210', accent: '#f7931a' },
+  lightning_node: { bg: '#0a0018', ground: '#1a1030', accent: '#ffdd00' },
+  satoshis_garage: { bg: '#0f0f0a', ground: '#1f1f14', accent: '#a0a080' },
+  mempool: { bg: '#100a18', ground: '#201828', accent: '#cc44ff' },
+  silk_road_ruins: { bg: '#0a0a0a', ground: '#181818', accent: '#338833' },
+  block_height_tower: { bg: '#080810', ground: '#181828', accent: '#4488dd' },
+  hodl_cave: { bg: '#080604', ground: '#1a1410', accent: '#f7931a' },
+  whale_pool: { bg: '#001020', ground: '#0a2040', accent: '#0088ff' },
+  node_farm: { bg: '#000a00', ground: '#0a1a0a', accent: '#22ff44' },
+  genesis_block: { bg: '#0a0a00', ground: '#1a1a10', accent: '#ffd700' },
+  pizza_day_parlor: { bg: '#1a0a00', ground: '#2a1a08', accent: '#ff6622' },
+  difficulty_adjustment: { bg: '#100810', ground: '#201820', accent: '#ff4488' },
+  fifty_one_percent: { bg: '#1a0000', ground: '#2a0808', accent: '#ff0000' },
+  timechain_temple: { bg: '#08080a', ground: '#18182a', accent: '#88aaff' },
+  nostr_relay_room: { bg: '#0a0014', ground: '#1a1028', accent: '#8844ff' },
 }
 
 const spriteAnims = {