Client builds capped on resources

v0.14.0-beta

Client builds capped on resources. Building a project's image (e.g. a next build, very hungry) now goes through a dedicated builder limited in CPU/memory (~1 CPU and 4 GB by default, adjustable). A build can therefore no longer saturate the shared server and trigger the host's CPU throttling, even on a large project or with several simultaneous builds (they share the same capped builder). Container runtime was already limited; the build step now is too. Visible effect: a build may be slightly slower, but it no longer brings the server to its knees.