feat: victory celebration animations

Normal wins: winner flex pose with camera flash bursts + confetti rain.
Upset wins (100+ Elo underdog): dramatic zoom on winner with golden
flash. Upset tag shown on win overlay. Wired into FightViewer after
KO/Perfect sequence.

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

frontend/src/components/FightViewer.vue

@@ -587,12 +587,19 @@ async function _doReplay() {
         await sleep(300) // let fatality voice finish
       }
 
+      // Victory celebration — detect upsets (winner had lower Elo)
+      const winnerElo = winningSide === 'a' ? (props.fight.botA?.eloRating ?? 1200) : (props.fight.botB?.eloRating ?? 1200)
+      const loserElo = winningSide === 'a' ? (props.fight.botB?.eloRating ?? 1200) : (props.fight.botA?.eloRating ?? 1200)
+      const isUpset = winnerElo < loserElo - 100
+      await scene.playVictoryCelebration(winningSide, isUpset)
+
       glitching.value = true
       sfxApplause()
       sfxCrowdCheer()
       await sleep(200)
       glitching.value = false
-      await showOverlay(`${winnerName} WINS!`, '#00f0ff', 1800)
+      const upsetTag = isUpset ? ' UPSET!' : ''
+      await showOverlay(`${winnerName} WINS!${upsetTag}`, isUpset ? '#ff6600' : '#00f0ff', 1800)
 
       logItems.value.push(
         { type: 'divider', round: 99, text: '', color: '' },