Feature/issue 287 k6 load tests

[mijinummi]

Description

This PR introduces automated performance testing via a k6 validation suite targeting our primary high-traffic endpoints (/status, /dashboard, and /leaderboard). A dedicated release gate workflow has been added to isolate latency regression testing on every incoming pull request and push to the main branch.

Changes

• Performance Workflows: Created .github/workflows/load-test.yml to orchestrate a background application stack runner and evaluate endpoints concurrently across a performance matrix.
• k6 Test Harness Suites: Added automated assertions under tests/load/ (health.js, dashboard.js, leaderboard.js) to enforce strict performance constraints.
• Latency Budget Enforcements: Bound release gates to a strict target threshold requiring P95 < 200ms (and 250ms for the complex dashboard query feed) alongside an error rate ceiling below 1%.

Testing Mitigations

• Workflow Simulation: Validated the operational execution loop including local container health checks and multi-stage dependency bootstrapping.
• Endpoint Verification: Checked threshold response parsing accuracy under baseline virtual user configurations.

Related Issues

Fixes #287

[YaronZaki]

LGTM