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/package.json

@@ -12,6 +12,7 @@
     "test": "vitest",
     "test:watch": "vitest watch",
     "test:e2e": "vitest run --config tests/integration/vitest.config.ts",
+    "test:perf": "vitest run --config tests/performance/vitest.config.ts",
     "typecheck": "tsc --noEmit",
     "lint": "eslint src/",
     "lint:fix": "eslint src/ --fix"