test(cli): add tests for tokenize and audit subcommands

[interview35]

The cli.py module had zero test coverage. This adds a new tests/test_cli.py with 7 tests exercising both subcommands:

• tokenize without --audio-codes encodes text with BOS/EOS boundaries
• tokenize with --audio-codes packs text + separator + audio tokens
• tokenize handles multi-byte UTF-8 characters correctly
• tokenize with empty text produces just BOS and EOS
• audit prints conversation and turn counts from a valid JSONL file
• audit with a nonexistent manifest exits with code 2
• Missing subcommand exits with code 2

All 7 tests pass locally (pytest tests/test_cli.py -q).