feat(integrations): pin optional ecosystem contracts (#237)

[codeforester]

Summary

• record immutable Bashly, Argc, Argbash, Bats, ShellCheck, and shfmt pins with explicit ownership boundaries
• add a networkless integration-release contract and keep bpkg/Basher/Basalt fail-closed until a verifiable GA asset and maintenance path exist
• track the Awesome Bash discovery submission as an honest post-GA draft

Validation

• ./tests/validate.sh
• tests/integration-release-contract.sh
• git diff --check

Fixes #237