feat: add packet filter support for network-level fault injection

Enhance troubleshooting injection skill with network-level fault injection capabilities:
- Add manage_gns3_packet_filter tool for link-level filtering
- Support latency, packet loss, corruption, and BPF-based traffic blocking
- Update fault selection to distinguish between configuration and network faults
- Improve documentation format to show both injection methods
- Add packet_filter_issues.yaml for defining network fault scenarios

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: yueguobin