Mission parser splits quoted --verify commands

## Problem

`parse_mission_args()` tokenizes Mission arguments with `raw_args.split()`. A quoted verification command containing spaces is split into separate tokens, so the verifier receives an invalid command and part of the command leaks into the task text.

## Reproduction

```text
parse_mission_args('Implement the feature --verify "pytest -q" --max-iterations 7')
# current result:
# {'task_text': 'Implement the feature -q"', 'verify_commands': '"pytest', 'max_iterations': 7}
```

Expected result:

```text
{'task_text': 'Implement the feature', 'verify_commands': 'pytest -q', 'max_iterations': 7}
```

## Proposed direction

Use quote-aware standard-library tokenization for valid Mission arguments, retain the existing whitespace-splitting behavior when quotes are malformed, and show the quoted multi-word form in the Mission help text. Add focused regression coverage for both paths.