feat: expand backend admin marketplace and scaling

PERFORMANCE_TESTING.md

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+# Performance Testing
+
+This project now includes built-in scripts to check correctness, startup time, endpoint latency, and basic load.
+
+## 1. Correctness first
+
+Run these before any performance test:
+
+```powershell
+npm run build
+npm test -- --runInBand
+npm run test:e2e -- --runInBand
+```
+
+## 2. Startup time
+
+Build the app, then measure cold start:
+
+```powershell
+npm run build
+npm run perf:startup
+```
+
+Optional parameters:
+
+```powershell
+node scripts/startup-benchmark.js --port 4200 --timeout 45000
+```
+
+## 3. Health endpoint load
+
+If the API is already running on port `4000`:
+
+```powershell
+npm run perf:health
+```
+
+This runs a simple GET benchmark against `http://127.0.0.1:4000/api/v1/health`.
+
+## 4. Custom endpoint load
+
+Examples:
+
+```powershell
+node scripts/load-test.js --url http://127.0.0.1:4000/api/v1/health --duration 20 --concurrency 50
+node scripts/load-test.js --url http://127.0.0.1:4000/api/v1/feed/trending --header "Authorization: Bearer YOUR_TOKEN" --duration 30 --concurrency 25
+node scripts/load-test.js --url http://127.0.0.1:4000/api/v1/auth/login --method POST --body "{\"email\":\"user@example.com\",\"password\":\"secret\"}" --duration 20 --concurrency 10
+```
+
+Supported options:
+
+- `--url`
+- `--method`
+- `--duration`
+- `--concurrency`
+- `--timeout`
+- `--warmup`
+- `--header "Key: Value"`
+- `--body`
+- `--body-file`
+
+## 5. What to watch
+
+- `requestsPerSecond`: throughput
+- `successRate`: percentage of successful requests
+- `non2xxCount`: server or validation failures
+- `timeoutCount`: slow requests
+- `latencyMs.p95` and `latencyMs.p99`: tail latency under load
+
+## 6. Practical test order
+
+1. `build`
+2. unit tests
+3. e2e tests
+4. startup benchmark
+5. health benchmark
+6. authenticated benchmarks for hot endpoints:
+   - `auth/login`
+   - `feed/me`
+   - `feed/trending`
+   - `posts`
+   - `chat/messages`
+   - `notifications`
+
+## 7. Real API benchmark examples
+
+Login:
+
+```powershell
+node scripts/load-test.js --url http://127.0.0.1:4000/api/v1/auth/login --method POST --header "Content-Type: application/json" --body "{\"email\":\"user@example.com\",\"password\":\"secret123\"}" --duration 20 --concurrency 10
+```
+
+Trending feed with bearer token:
+
+```powershell
+node scripts/load-test.js --url http://127.0.0.1:4000/api/v1/feed/trending --header "Authorization: Bearer YOUR_ACCESS_TOKEN" --duration 30 --concurrency 25
+```
+
+Authenticated user feed:
+
+```powershell
+node scripts/load-test.js --url http://127.0.0.1:4000/api/v1/feed/me?limit=20 --header "Authorization: Bearer YOUR_ACCESS_TOKEN" --duration 30 --concurrency 15
+```
+
+Notifications:
+
+```powershell
+node scripts/load-test.js --url http://127.0.0.1:4000/api/v1/notifications --header "Authorization: Bearer YOUR_ACCESS_TOKEN" --duration 20 --concurrency 15
+```
+
+## 8. Limits
+
+These scripts are useful local benchmarks, not full production profiling. They do not replace:
+
+- database profiling
+- CPU and memory profiling
+- distributed load tools like k6 or Gatling
+- multi-instance tests behind a reverse proxy