test(ci): raise shell coverage and close targeted prompts-submodule branch gaps

[CodeMonkeyCybersecurity]

Summary

PR #67 adds targeted shell-library tests to increase coverage and cover currently untested fallback and error branches in prompts-submodule helpers. The work should track an issue directly so the PR is linked cleanly.

Scope

• add targeted unit tests for uncovered branches in shell helpers
• raise shell coverage to the current target without padding unrelated lanes
• verify the added tests run in npm run ci and the focused shell test suites

Acceptance Criteria

• previously uncovered branches called out in PR test(ci): raise shell coverage to 95% with targeted branch tests #67 are exercised by tests
• shell coverage increases measurably and the repo coverage floor still passes
• PR test(ci): raise shell coverage to 95% with targeted branch tests #67 references this issue

Refs PR #67