Bootstrap Base Platform Tools repository

[codeforester]

Summary

• Bootstrap the public Base Platform Tools repository as a Base-managed project.
• Add README, CONTRIBUTING, CHANGELOG, LICENSE, and the initial project manifest.
• Add tooling boundary documentation for separating Base core from optional platform/SRE utilities.
• Add repository validation, GitHub Actions, a PR template, and baseline ignore rules.

Issue

Closes codeforester/base#480

Validation

• tests/validate.sh
• git diff --check
• /Users/rameshhp/work/base/bin/basectl test base-platform-tools

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

Platform Support

• Repository scaffold is platform-neutral.
• CI validation currently runs on Ubuntu.
• No platform utility CLIs are added in this PR.
• Future tools must document their supported platforms and fail clearly on unsupported platforms.

Notes

• Existing caff and sort utilities remain in codeforester/base for now.
• Future migration of those utilities should happen through separate issues and PRs after this repository baseline is stable.