feat: spectator reactions with floating emoji particles

POST /api/fights/:fightId/react endpoint accepts emoji reactions (fist,
fire, skull, 100, clown), aggregates counts, broadcasts via SSE.
Reaction bar added to FightViewer with floating emoji particles that
rise and fade. Live fight views receive reactions via SSE in real-time.

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

server/src/routes/fights.ts

@@ -15,6 +15,10 @@ export const fightsRouter = new Hono()
 // Track spectator counts per fight
 const spectatorCounts = new Map<string, number>()
 
+// Track reactions per fight
+const VALID_REACTIONS = new Set(['fist', 'fire', 'skull', '100', 'clown'])
+const fightReactions = new Map<string, Record<string, number>>()
+
 export function getSpectatorCount(fightId: string): number {
   return spectatorCounts.get(fightId) || 0
 }
@@ -383,3 +387,31 @@ fightsRouter.get('/:id/stream', (c) => {
     }
   })
 })
+
+// React to a fight
+fightsRouter.post('/:id/react', async (c) => {
+  const fightId = c.req.param('id')
+  const body = await c.req.json<{ emoji?: string }>()
+  const emoji = body?.emoji
+
+  if (!emoji || !VALID_REACTIONS.has(emoji)) {
+    return c.json({ error: 'Invalid reaction. Use: fist, fire, skull, 100, clown' }, 400)
+  }
+
+  // Aggregate
+  if (!fightReactions.has(fightId)) {
+    fightReactions.set(fightId, {})
+  }
+  const counts = fightReactions.get(fightId)!
+  counts[emoji] = (counts[emoji] || 0) + 1
+
+  // Broadcast via SSE
+  fightEvents.emit({
+    fightId,
+    type: 'reaction',
+    data: { emoji, counts: { ...counts } },
+    timestamp: new Date().toISOString(),
+  })
+
+  return c.json({ ok: true, counts })
+})