feat: add 160 Bitcoin-themed prompts across all 16 challenge types

10 prompts per type covering Bitcoin history, mining, Lightning,
privacy, culture, memes, riddles, and technical knowledge.
Total prompts: 1,485 (253 Bitcoin-themed).

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

server/src/engine/challenges.ts

@@ -1,5 +1,6 @@
 import { TEMPLATES, type ChallengeTemplate, type PromptEntry, type PromptTheme, type PromptDifficulty } from './challenge-data.js'
 import { EXTRA_PROMPTS } from './challenges-extra.js'
+import { BITCOIN_PROMPTS } from './challenges-bitcoin.js'
 import { pick } from '../lib/utils.js'
 
 export interface Challenge {
@@ -21,6 +22,8 @@ export type { ChallengeTemplate, PromptEntry, PromptTheme, PromptDifficulty }
 for (const t of TEMPLATES) {
   const extras = EXTRA_PROMPTS[t.type]
   if (extras) t.prompts.push(...extras)
+  const btc = BITCOIN_PROMPTS[t.type]
+  if (btc) t.prompts.push(...btc)
 }
 
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