refactor: share config command test isolation

[vincentkoc]

What Problem This Solves

Removes repeated config-path isolation setup from 36 config command tests.

Why This Change Was Made

Introduces one test helper that preserves the existing environment-clearing, temporary-directory, config-path, HOME, XDG_CONFIG_HOME, and CRABBOX_CONFIG setup in the same order. All assertions, environment sentinels, config bytes, negative tests, test names, errors, JSON checks, and application invocations remain unchanged.

User Impact

No user-visible behavior change. This is a test-only refactor that removes 169 lines of duplicated setup.

Evidence

• Replaced 36 byte-identical setup blocks: 7 config-set tests and 29 config-show tests.
• Inverse reconstruction of every helper call reproduced the original file byte-for-byte, including comments and spacing.
• Verified gofmt and git diff --check.
• Confirmed the concurrent Parallels redaction change in fix(parallels): macOS leases connect when Tools cannot report the guest #1745 is outside the changed setup blocks.
• Local Go tests were not run due to host budget policy.
• Full hosted pull-request CI is pending.

[clawsweeper]

🦞👀
ClawSweeper picked this up.

Pull request received. I will update this pull request when review starts.

ClawSweeper review blocked

Automated review did not run, so no review verdict was produced.

Reason: The input-safety check rejected material in this revision. No detected value, path, or scanner output is reproduced here.

ClawSweeper will not retry this unchanged revision.

Next step: If this is a genuine credential, remove and rotate it. If it is an intentional test fixture, a maintainer must review and qualify it.

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