tests: add coverage for paths-common and refactored shell entrypoints

[benvinegar]

Problem

The new shared helper bin/lib/paths-common.sh is central to path derivation, but there is no dedicated test file for it. Several refactored scripts also lack direct shell regression coverage.

This leaves high-impact path override behavior under-tested.

Proposed solution

• Add bin/lib/paths-common.test.sh covering:
  • defaults via bb_init_paths
  • env override behavior
  • bb_refresh_release_paths with/without force
• Add focused tests for refactored entrypoints (or helper extraction + tests) for:
  • bin/deploy.sh
  • bin/doctor.sh
  • bin/setup-firewall.sh
  • bin/uninstall.sh
• Ensure new tests are wired through existing unified test runners.

Helpful context

Existing helper shell tests:

• bin/lib/deploy-common.test.sh
• bin/lib/doctor-common.test.sh
• bin/lib/json-common.test.sh

Current gap:

• no bin/lib/paths-common.test.sh
• broad script-level coverage exists for update/rollback but not these newly refactored entrypoints.