Seed CLI layer scaffold

[codeforester]

Summary

• Seed the CLI layout for future Bash and Python Base Platform Tools.
• Document that this repo reuses Base basectl and base-wrapper instead of copying them.
• Add launcher conventions for Bash runtime scripts and Python package execution through the base-platform-tools project venv.
• Add cli-check as a manifest-declared validation command.
• Extend repository validation to assert the CLI scaffold and docs.

Issue

Closes #2

Validation

• tests/validate.sh
• git diff --check
• bash -n tests/validate.sh
• /Users/rameshhp/work/base/bin/basectl test base-platform-tools
• /Users/rameshhp/work/base/bin/basectl run base-platform-tools --list
• /Users/rameshhp/work/base/bin/basectl run base-platform-tools cli-check

basectl test and basectl run ... cli-check report the expected warning that the project venv has not been created yet because basectl setup base-platform-tools has not been run, then delegate to tests/validate.sh successfully.

Platform Support

• Scaffold and docs are platform-neutral.
• No production utility CLI is added in this PR.
• Future tools must document their supported platforms and fail clearly on unsupported platforms.

Notes

• This PR does not migrate caff or sort.
• This PR does not copy basectl or base-wrapper into base-platform-tools.