[danjboyd]

ConfigTests creates temporary app roots without consistently removing them, contributing to #210. Register a teardown block in its local createTempAppRoot helper so every successful allocation is removed, including after an assertion failure. Existing explicit cleanup remains compatible.

Only tests/unit/ConfigTests.m changes. The shared ALNTestTemporaryDirectory helper, test lifecycle implementation and production code are untouched. Other fixture leaks in #210 remain outside this PR.

Validation on the existing pinned Debian 13 amd64 normal runtime, in a separate worktree based on main e26a755e:

• Original focused ConfigTests bundle: 19 passed, zero skips/failures; 14 fixture directories remained in an isolated temp directory.
• Changed focused ConfigTests bundle: 19 passed, zero skips/failures; zero fixture directories remained.
• git diff --check passed. This is focused Linux validation; no new Windows/macOS test execution is claimed.

Draft for Dan’s review. This is a partial fixture cleanup, with no issue closure or production/release changes.