'bottles' was the package name when it held a single Bottle Protocol;
since we added BottlePlatform / BottlePlan / BottleCleanupPlan and
made it the home of platform dispatch, 'platform' describes the
package better. The 'bottle' concept (and the manifest field) stays.
CLI imports update from ..bottles to ..platform; internal relative
imports inside the package survive the rename unchanged. Git
detected all 7 file renames.
