Consume shared GitHub Bash helpers

[codeforester]

Summary

• Delegate Base's generic GitHub Bash primitives to the shared helpers in base-bash-libs.
• Keep Base-specific command behavior in place while removing duplicate default-branch, repo-origin, branch, and worktree parsing code.
• Pin CI to base-bash-libs commit d62e8c1fec2de9148bc832977c206b9f1827dd19, which includes the helper shadowing fix found during this migration.

Fixes #1488.

Validation

• RED: env BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats cli/bash/commands/basectl/tests/gh.bats cli/bash/commands/basectl/tests/repo.bats failed on the new delegation assertions before implementation.
• PASS: env BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats cli/bash/commands/basectl/tests/gh.bats cli/bash/commands/basectl/tests/repo.bats
• PASS: bash -n cli/bash/commands/basectl/subcommands/gh.sh cli/bash/commands/basectl/subcommands/repo.sh cli/bash/commands/basectl/tests/gh.bats cli/bash/commands/basectl/tests/repo.bats
• PASS: shellcheck -S warning cli/bash/commands/basectl/subcommands/gh.sh cli/bash/commands/basectl/subcommands/repo.sh
• PASS: git diff --check
• PASS: env -u BASE_HOME BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash BASE_CACHE_DIR=/private/tmp/base-pr-train-1488-rerun ./bin/base-test
• PASS: env PYTHONPATH=lib/python:cli/python $HOME/.base.d/base/.venv/bin/python -m pytest tests/test_github_workflows.py