feat(report): Advisory field for pending severity (#1765)

[FabioLeitao]

Summary

• Add Advisory to the Excel Report info About table, next to Integrity state (#856 family): about.get("advisory", "unknown").
• Loud text only — same spirit as -alpha. No refuse path, no trust clamp, no change to trust_level.
• Air-gap / missing payload → unknown (never empty, never none). Beacon-shaped payload with no sev → none. Pending sev → e.g. sev=critical · 1.7.4 → 1.7.6 · fix disponível · visto em ….
• Scanner still does not call the beacon; _release_advisory_payload() is fail-open (None today) so reports keep generating.

Closes #1765

Test plan

• Negative proof: with production Advisory row absent, test_report_info_advisory_* failed (KeyError: 'Advisory').
• After the row: pending severity shows the alert string; absent key → unknown and _build_report_info / generate_report still succeed.
• ./scripts/check-all.sh OK on this branch.

[strix-security]

Strix Security Review

No security issues found.

_{Updated for dd813c7.}

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Reviewed by Strix
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