Check feature membership with merge-base before telling a user it's in a build

When several integration branches exist (a feature-integration branch, a release stack, the main branch), don't assume a reviewed feature is in a given test build. Run git merge-base --is-ancestor <feature-tip> <build-sha> for that build. A user asked whether a per-file settings feature was in their test app. It had passed review and compiled, but only on a different stack branch, not the one the app was built from. That explained the behaviour they saw at once. Also read the build's embedded commit (e.g. an Info.plist key) to confirm what was actually built.