fix: write catalog cache atomically

[itzptk]

Summary

• Write catalog-cache.json through a sibling temporary file before renaming it into place.
• Remove the temporary file if writing or renaming fails so interrupted refreshes do not corrupt the previous cache.
• Add a Vitest regression test that simulates an interrupted replacement write and verifies the previous cache still reads.

Closes #18

Verification

• RED: npm run test:node -- catalog-cache failed before the fix with expected null to deeply equal previous.
• GREEN: npm run test:node -- catalog-cache → 1 test passed.
• npm run test:node → 16 files passed, 117 tests passed.
• npm run build → Angular production build and Electron tsup build succeeded.