feat(agent): add code porting/translation patterns (fluent_cli-9uvj)

Implement CodePortingPatternDetector with:
- 8 built-in language pair patterns (C→Rust, C++→Rust, Python→Rust, Python→Go, JS→TS, Java→Kotlin, C→Go, Ruby→Python)
- Type and stdlib mappings for each language pair
- Word boundary matching for accurate language detection
- Stricter porting task detection to avoid false positives
- 7 unit tests covering detection, augmentation, and edge cases

This enables the agent to provide context-aware guidance when detecting code porting tasks.

Author: njfio