Move round scheduler in-app via instrumentation.ts, remove cron endpoint

Round open/close scheduling now runs as a 60s setInterval inside the
app process (via instrumentation.ts register hook) instead of needing
an external crontab. Removed the /api/cron/round-scheduler endpoint.

- DRAFT rounds auto-activate when windowOpenAt arrives
- ACTIVE rounds auto-close when windowCloseAt passes
- Uses existing activateRound/closeRound from round-engine

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

src/instrumentation.ts

@@ -25,5 +25,19 @@ export async function register() {
           })
       })
       .catch(() => {})
+
+    // Round scheduler: check every 60s for rounds that need to open/close
+    import('./server/services/round-scheduler')
+      .then(({ processScheduledRounds }) => {
+        console.log('[Startup] Round scheduler started (60s interval)')
+        // Run once immediately, then every 60 seconds
+        processScheduledRounds().catch(() => {})
+        setInterval(() => {
+          processScheduledRounds().catch((err) => {
+            console.error('[RoundScheduler] Error:', err)
+          })
+        }, 60_000)
+      })
+      .catch(() => {})
   }
 }