threat-model-authoring

Draft phase 3.5 of a threat model from the orientation brief, surface analysis, and maintainer answers. USE WHEN writing threat-model.md to the canonical §1.1–§1.19 structure. Combines concise prose with the §1.7 trust table and contract matrix, §1.8 output statements, §1.17 disposition table, §1.1 triager quick-start, and any prior-policy back-map. Tags every non-trivial claim as documented, maintainer, or…