feat(release): RELEASE identity + image tag single-sourcing (#10)

- RELEASE file: single source of release version (0.0.X until declared stable)
- common.sh load_release(): validates version, derives
  MOSAIC_IMAGE_TAG=mosaic-poc-agent:<pi>-r<release> from the pinned pi dep
- compose.yaml: image tag is required env; build/hello/verify call load_release
- verify.sh derives the image name instead of hardcoding it
- package.json version aligned to the same 0.0.X line

Closes #10

scripts/build.sh

@@ -6,6 +6,7 @@ cd "$(dirname "$0")/.."
 source scripts/common.sh
 
 load_config
+load_release
 
 bootstrap_runtime_dir