Declared sandbox build targets

- Gradle exposes Bukkit, API, SPI, and loader targets with isolated build requirements
- Build tasks retain verified artifacts inside their project directories
- API generation writes a jar without publishing or external copies
- Captured source hashes identify sandbox builds
- Build instructions describe manager deployment

build-all.sh

@@ -1,4 +1,4 @@
 #!/usr/bin/env bash
 set -euo pipefail
 cd "$(dirname "$0")"
-./gradlew buildAllToOut --no-parallel -PuseLocalVolmLib=false "$@"
+./gradlew buildAll "$@"