Makes the contributor profile actually fast: with OMNIROUTE_BUILD_PROFILE=contributor the build stops after next build instead of copying docs/ and running assembleStandalone, which is the expensive half and produces an artifact contributors never ship. Adds isContributorBuild() next to the existing isBackendOnlyBuild() and documents the compile-only contract in CONTRIBUTING.md.
Reconciled on merge: CONTRIBUTING.md's new paragraph was inside the ```bash fence and would have rendered as shell — moved below the closing fence. package.json auto-merged against the tip.
Verified: contributor-build-script + backend-only-smoke-workflows 10/10 green.
Thanks @rafacpti23.