fix: human fight UX — SSE challenge input, fighter sprites, battle log questions, left-side positioning

- Add SSE human_challenge listener for instant input activation with auto-focus
- Buffer challenges during 3s round cooldown, apply with correct remaining time
- Map 'human' archetype to fighter-looking archetypes (boxer, ninja, etc.) in sprite system
- Show challenge questions in battle log via round_start SSE events
- Ensure human players are always botA (left side) in queue matchmaking

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

server/src/engine/queue.ts

@@ -91,8 +91,11 @@ export async function joinQueue(botId: string): Promise<string> {
     const opponent = waitingQueue.shift()!
     clearTimeout(opponent.timeoutHandle)
 
-    // Start the fight
-    const fightId = await startFight(opponent.botId, botId)
+    // Start the fight — ensure human players are always botA (left side)
+    const isHumanJoiner = bot.webhookUrl === 'http://human.local/'
+    const fightId = isHumanJoiner
+      ? await startFight(botId, opponent.botId)
+      : await startFight(opponent.botId, botId)
     opponent.resolve(fightId)
     return fightId
   }