Release base-bash-libs v1.2.0

[codeforester]

Context

Base now imports the shared GitHub CLI helpers added to base-bash-libs after v1.1.0. The library needs a published v1.2.0 release so Base can depend on a released helper surface.

Scope

• Bump base-bash-libs from 1.1.0 to 1.2.0.
• Move the unreleased changelog entries into the 1.2.0 release section.
• Verify the library validation suite.
• Publish the v1.2.0 GitHub release after the release PR merges.

Acceptance Criteria

• VERSION reports 1.2.0.
• CHANGELOG.md has a dated 1.2.0 section.
• Library validation passes locally and in CI.
• GitHub release v1.2.0 exists and points at the merged release commit.