Add firewall rule evidence fixtures

[jddark62]

Summary

Adds a structured rule evidence matrix to firewall-review so findings are tied to concrete source-of-truth evidence before severity is assigned.

This includes:

• Evidence confidence levels for source-controlled policy, exported config, runtime/log evidence, screenshots, stale exports, and missing evidence.
• Not Evaluable reason codes for missing object expansion, runtime counters, NAT or route context, IPv6 policy, egress path, export freshness, owner/ticket evidence, and logging proof.
• Output fields for evidence confidence, Not Evaluable reasons, IPv6 default-deny status, and NAT/related policy context.
• Seven YAML calibration fixtures covering controlled private traffic, object-group expansion, missing expansions, counter reset baselines, NAT exposure, missing IPv6 policy, and missing SIEM/log destination proof.

Validation

• git diff --check
• Skill frontmatter YAML parse
• Fixture YAML parse: 7 YAML blocks
• Markdown fence balance check
• Public-file privacy scan

/claim #59

Payment details can be coordinated privately after maintainer acceptance.