[FonaTech]

Summary

Two driver fixes, found while testing translate.py from a fresh directory after the enzh-50m-sft-v1 release.

• --download on python.org macOS Python. That build ships no system CA bundle, so urlretrieve failed with CERTIFICATE_VERIFY_FAILED. The fix:
  • download() now uses certifi's CA bundle when it is installed. certifi comes in through the transformers → huggingface_hub → httpx dependency chain.
  • A failed download removes the partial file.
  • The error message says how to fetch the weights by hand.
• Refusing input before loading. Chinese input was previously reported as "weights not found" whenever the weights were absent. The CLI now runs the language check before it builds the Translator, so out-of-boundary input is refused with exit code 2 and nothing is loaded or downloaded.

Test plan

• ruff==0.17.4 and flake8 --select=E9,F63,F7,F82 are clean.
• CI simulation, no MLX: 264 passed / 49 skipped on main, 410 passed / 67 skipped on dev.
• There are 2 new tests:
  • Chinese input is refused when the weights are absent.
  • A failed download leaves no .part file.
• The driver was run from a fresh directory. GitHub release assets resolve to ::1 on the test machine, so a localhost server provided the weights:
  • The download passes the SHA-256 check, and a file with a wrong hash is rejected.
  • MLX and torch-CPU translations work.
  • zh and --direction zh_en exit with code 2.
  • The first 120 FLORES+ devtest outputs match the published run exactly.
• The release assets' GitHub digests equal the local SHA-256 57c59a14…fab4b7.

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