Monorepo CI overview

Monorepo CI as a cross-cutting topic - running efficient continuous integration in repositories that contain multiple packages, services, or applications. Covers affected-graph computation (Nx, Turborepo, Bazel) to run only impacted tests, workspace-aware caching, per-package pipeline definitions, dependency ordering for build fan-out, and change-set-based deployment gating. Addresses the tension between monorepo developer ergonomics and pipeline execution cost.