fix(warp): allow for native multiplatform with warp

[gondoi]

Warp wasn't using their required action file to allow for correct multi-arch setup.

[cursor]

PR Summary

Medium Risk
Changes the build-backend: warp build/push execution path and introduces new timeout/API-key wiring, which could break CI image publishing if inputs/secrets are misconfigured.

Overview
Fixes build-backend: warp in docker-build-push.yml to build/push images via Warpbuilds/build-push-action@v6 (while keeping the in-repo composite for registry auth + docker/metadata-action only), enabling correct multi-platform behavior with Warp Docker Builders.

Adds optional WARPBUILD_API_KEY workflow secret plus configurable builder wait time (warp-builder-timeout-ms / warp-timeout-ms) and updates docs/examples to clarify runner vs builder responsibilities and required Warp profile/arch settings.

^{Reviewed by Cursor Bugbot for commit 36ff6e6. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit d620470. Configure here.}