feat: add narrations for all 16 challenge types, eliminate generic fallback

Add dedicated narrations for: magic_duel, sports_showdown, vehicle_mayhem,
nature_clash, animal_kingdom, hack_battle (6 per type, 36 new narrations).
All 16 challenge types now have themed narrations — no generic fallback needed.
Add narration variety test verifying >1 unique narration per type.

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

server/src/engine/scoring.test.ts

@@ -409,3 +409,32 @@ describe('creative scoring spam detection', () => {
     expect(result.botBScore).toBeGreaterThan(2)
   })
 })
+
+describe('narrations', () => {
+  const allTypes = [
+    'speed_blitz', 'math_blitz', 'riddle', 'hallucination_check', 'trap_card',
+    'magic_duel', 'sports_showdown', 'vehicle_mayhem', 'nature_clash', 'animal_kingdom',
+    'hack_battle', 'roast_battle', 'creative_writing', 'meme_war', 'code_golf', 'wrestling_match',
+  ]
+
+  it('all 16 challenge types produce varied narrations', () => {
+    const botA = { id: 'a1', name: 'AlphaBot' }
+    const botB = { id: 'b1', name: 'BetaBot' }
+
+    for (const type of allTypes) {
+      const challenge = makeChallenge({ type, scoring: 'factual' })
+      const narrations = new Set<string>()
+      for (let i = 0; i < 20; i++) {
+        const result = scoreRound(
+          challenge, botA, botB,
+          makeResponse('4', 500),
+          makeResponse('banana', 500),
+          null, 0, 0,
+        )
+        narrations.add(result.narration)
+      }
+      // Should have variety (>1 unique narration across 20 rounds)
+      expect(narrations.size).toBeGreaterThan(1)
+    }
+  })
+})