Clean up main test temp roots

[ken-jo]

Motivation

Four test fixture paths created temporary directories without transferring ownership to teardown. Successful and failing runs could therefore leave crash-report and whitelist-cache roots behind.

Scope

• register each crash-reporter user-data root immediately when it is created
• register every whitelist-cache root created by the shared fixture helper
• reset the registry singleton before removing its cache roots
• remove all registered roots through the shared async Windows-lock-aware teardown helper
• keep runtime behavior and existing assertions unchanged

Risk

Low. This is test-only lifecycle cleanup; no production code changes.

Validation

• bun run test:vitest -- src/main/__tests__/release-prep.test.ts src/main/host-api/__tests__/resolve-api-key.test.ts (56 passed)
• bun run typecheck
• bun run check:typecheck-tests
• bun run check:test-duplicates -- --fail-on-duplicates
• git diff --check
• pre-push test-only gate: typecheck, typecheck gate self-test, test typecheck ratchet, duplicate-helper policy, Electron ABI probe, 56 targeted tests