Replace per-switch network simulation with aggregate per-DC statistical model

Eliminates the 22K-object switchRegistry that caused O(n×m) scans 4x per tick.
Network health is now tracked as aggregate counts per tier (totalByTier/healthyByTier)
with RepairBatch timers, cutting late-game tick cost from ~50ms to ~0.3ms.

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

apps/web/src/pages/InfrastructurePage.tsx

@@ -162,7 +162,8 @@ function CohortStageBreakdown({ cohorts }: { cohorts: DeploymentCohort[] }) {
 
 function NetworkHealthIndicator({ dc }: { dc: DataCenter }) {
   const ns = dc.networkSummary;
-  if (ns.switchIds.length === 0) return null;
+  const torTotal = ns.totalByTier?.tor ?? 0;
+  if (torTotal === 0) return null;
 
   const hasDisconnected = ns.racksDisconnected > 0;
   const hasDegraded = ns.racksDegraded > 0;