feat: Added k6 performance tests

README.md

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+# K6 Load Tests
+
+Load tests for NowChess using K6 framework.
+
+## Installation
+
+```bash
+# Install K6 - https://k6.io/docs/getting-started/installation/
+# macOS
+brew install k6
+
+# Ubuntu/Debian
+sudo apt-get install k6
+
+# Windows (Chocolatey)
+choco install k6
+```
+
+## Running Tests
+
+### Smoke Test
+One user, basic journey validation.
+```bash
+k6 run simulations/smokeTest.js
+```
+
+### Load Test
+Ramp up to max users over duration.
+```bash
+BASE_URL=http://localhost:8080 MAX_USERS=5 RAMP_DURATION=60 k6 run simulations/loadTest.js
+```
+
+### Stress Test
+Incrementally increase users in steps.
+```bash
+BASE_URL=http://localhost:8080 \
+  START_USERS=2 \
+  USERS_INCREMENT=2 \
+  STEPS=2 \
+  STEP_DURATION=30 \
+  RAMP_DURATION=10 \
+  k6 run simulations/stressTest.js
+```
+
+### Spike Test
+Baseline → spike → baseline.
+```bash
+BASE_URL=http://localhost:8080 \
+  BASELINE_USERS=2 \
+  BASELINE_DURATION=20 \
+  SPIKE_USERS=15 \
+  k6 run simulations/spikeTest.js
+```
+
+### Endurance Test
+Constant load over long duration.
+```bash
+BASE_URL=http://localhost:8080 \
+  CONCURRENT_USERS=3 \
+  DURATION=300 \
+  k6 run simulations/enduranceTest.js
+```
+
+## Environment Variables
+
+- `BASE_URL` - API base URL (default: `http://localhost:8080`)
+- `AUTH_TOKEN` - Optional Bearer token for global auth
+- Test-specific variables documented in each simulation file
+
+## Output
+
+Results summary printed to console. For detailed metrics, use K6 output options:
+
+```bash
+# JSON output
+k6 run --out json=results.json simulations/smokeTest.js
+
+# Cloud output (requires K6 Cloud account)
+k6 run --out cloud simulations/smokeTest.js
+
+# InfluxDB + Grafana
+k6 run --out influxdb simulations/smokeTest.js
+```
+
+## Structure
+
+- `config.js` - Shared configuration, headers, checks
+- `scenarios/` - Reusable scenario definitions
+- `simulations/` - Test simulations with load profiles