Generate AGPL licenses for new repos

[codeforester]

Summary

• Make basectl repo init generate AGPL-3.0-or-later license notices for new repos.
• Reuse Base's bundled root AGPL text so generated licenses stay aligned with Base.
• Update repo-init docs, changelog, and BATS expectations.

Issue

Fixes #727

Validation

• bats cli/bash/commands/basectl/tests/repo.bats (red before implementation; failed on expected AGPL assertions)
• bats cli/bash/commands/basectl/tests/repo.bats
• git diff --check
• git diff --cached --check
• env -u BASE_HOME ./bin/base-test

Demo Impact

None. Repository scaffolding behavior only.

Notes

This follows the Base relicensing in #729 / #726 and changes future repo scaffolding defaults only.