Enforce documented CI compatibility

[KakkoiDev]

What changed

• test the documented tmux 3.0+ compatibility floor in the Linux matrix
• add a macOS job that runs unit and integration tests under the system Bash 3.2
• make ShellCheck blocking and resolve the existing findings
• update a stale lifecycle assertion to match the TSV data contract

Why

CI previously started at tmux 3.2, ran only on modern Ubuntu Bash, and ignored ShellCheck failures despite documenting tmux 3.0+ and Bash 3.2+ support.

Validation

• shellcheck scripts/*.sh
• 49 unit tests passed
• full 447-test integration run exercised the changes; its one stale assertion was corrected
• corrected lifecycle suite: 54/54 passed
• workflow YAML parse and git diff --check passed