test(#229): Add performance test suite for orchestrator

Add 14 performance benchmarks across 3 test files:
- Spawner throughput: single/sequential/concurrent spawn latency,
  session lookup, list performance, memory efficiency
- Queue service: backoff calculation throughput, validation perf
- Secret scanner: content scanning throughput, pattern scalability

Adds test:perf script to package.json.

Fixes #229

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/orchestrator/tests/performance/vitest.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    globals: true,
+    environment: "node",
+    include: ["**/*.perf-spec.ts"],
+    testTimeout: 60000,
+  },
+});