Monorepo CI on GitHub Actions

One-line changes trigger a full-repository build.

Why it happens

There is no affected-target detection, so CI treats every push as a change to everything.

What to change

1. Adopt affected detection — nx affected, turbo --filter, bazel query or pants --changed-since
2. Use path filters so unrelated workflows do not trigger at all
3. Share one warm cache across every package rather than caching per package
4. Run the task graph on a single large runner instead of many small ones

Monorepo on runnerhut

jobs:
  affected:
    runs-on: runnerhut-32vcpu-ubuntu-2404
    steps:
      - uses: actions/checkout@v4
        with: { fetch-depth: 0 }
      - run: npx nx affected -t lint test build --base=origin/main --parallel=16

The only runnerhut-specific line is `runs-on: runnerhut-32vcpu-ubuntu-2404`. Everything else is standard GitHub Actions — the same actions, the same secrets and the same permissions model you use today.