feat(CI): init

[devdumpling]

Summary

• Add GitHub Actions CI workflow for pull requests to main
• Add separate non-blocking load test workflow

Details

ci.yml - Main CI (blocking, ~2-3 min)

• Tier 1 (parallel): lint, test-sdk, test-api, test-dashboard, bench-size
• Tier 2 (sequential): integration tests with Postgres service container

load-test.yml - k6 load tests (non-blocking)

• Runs k6 throughput test + validates DB persistence
• Uses continue-on-error: true so failures don't block PRs

Both workflows use:

• Node 24 + pnpm with caching
• Gleam 1.6 / OTP 27 via erlef/setup-beam
• Postgres 16-alpine service container
• dbmate for migrations

Test plan

• CI workflow runs on this PR
• All jobs pass (lint, tests, size check, integration)
• Load test workflow runs (non-blocking)