feat: ranked queue Elo-bracket matchmaking and harder prompts

Elo-bracket matchmaking: prefer ±200, widen by 100 every 15s of waiting.
Add pickRankedChallenge() that filters to creative/open-ended only, never
multiple choice. Show ranked queue status, wait estimate, and "HARDER
PROMPTS" notice on JoinBoutPage.

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

server/src/engine/ranked-queue.ts

@@ -26,8 +26,11 @@ export function setRankedCooldown(botId: string) {
   rankedCooldowns.set(botId, Date.now() + COOLDOWN_MS)
 }
 
-export function getRankedQueueStatus(): { waiting: number } {
-  return { waiting: rankedQueue.length }
+export function getRankedQueueStatus(): { waiting: number; estimatedWaitSec: number } {
+  const waiting = rankedQueue.length
+  // If someone is waiting, new joiner matches instantly; otherwise estimate ~15s
+  const estimatedWaitSec = waiting > 0 ? 5 : 15
+  return { waiting, estimatedWaitSec }
 }
 
 /**
@@ -94,21 +97,38 @@ export async function joinRankedQueue(botId: string, paymentId: string): Promise
     old.reject(new Error('Rejoined ranked queue'))
   }
 
-  // Check if someone is already waiting — instant match by closest ELO
+  // Elo-bracket matchmaking: prefer opponents within bracket, widen over time
   if (rankedQueue.length > 0) {
-    rankedQueue.sort((a, b) => {
-      const diffA = Math.abs(a.eloRating - bot.eloRating)
-      const diffB = Math.abs(b.eloRating - bot.eloRating)
-      return diffA - diffB
-    })
+    const now = Date.now()
+    // Find best match: base bracket ±200, widens by 100 every 15s of waiting
+    let bestMatch: RankedQueueEntry | null = null
+    let bestDiff = Infinity
 
-    const opponent = rankedQueue.shift()!
-    clearTimeout(opponent.timeoutHandle)
+    for (const entry of rankedQueue) {
+      const waitSec = (now - entry.joinedAt) / 1000
+      const bracket = 200 + Math.floor(waitSec / 15) * 100
+      const eloDiff = Math.abs(entry.eloRating - bot.eloRating)
+      if (eloDiff <= bracket && eloDiff < bestDiff) {
+        bestMatch = entry
+        bestDiff = eloDiff
+      }
+    }
 
-    // Start ranked fight and link both payments
-    const fightId = await runFightAsync(opponent.botId, botId, 'ranked')
-    await linkPaymentsToFight(fightId, [opponent.paymentId, paymentId])
-    opponent.resolve(fightId)
+    // If no one in bracket, fall back to closest overall
+    if (!bestMatch) {
+      rankedQueue.sort((a, b) =>
+        Math.abs(a.eloRating - bot.eloRating) - Math.abs(b.eloRating - bot.eloRating)
+      )
+      bestMatch = rankedQueue[0]
+    }
+
+    const idx = rankedQueue.indexOf(bestMatch)
+    rankedQueue.splice(idx, 1)
+    clearTimeout(bestMatch.timeoutHandle)
+
+    const fightId = await runFightAsync(bestMatch.botId, botId, 'ranked')
+    await linkPaymentsToFight(fightId, [bestMatch.paymentId, paymentId])
+    bestMatch.resolve(fightId)
     return fightId
   }