Improve segmentation egress boundary gates

[yZangEren]

Closes #1685.

Scope

• Adds v1.1.0 egress boundary guidance to skills/network/segmentation/SKILL.md.
• Adds discovery patterns for NAT, egress, proxy, DNS, resolver, and service-mesh artifacts.
• Adds a dedicated egress boundary and internet exit evidence step covering:
  • approved destination inventory;
  • enforcement point proof;
  • direct internet route and bypass review;
  • DNS path controls;
  • port-only outbound allowlist handling;
  • logging and exception lifecycle evidence.
• Adds an Egress Boundary Matrix to the output template.
• Updates findings classification and common pitfalls for unrestricted egress, proxy/DNS/service-mesh bypasses, broad NAT routes, and stale exceptions.

Validation

• git diff --check
• Markdown fence-balance check: 8 fences, balanced
• ASCII check: 0 non-ASCII characters
• Required marker checks for SEG-EGRESS-01, Egress Boundary Matrix, Direct Internet Route Review, and 1.1.0

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