CDN-216: The Provenance Gate

CDN-216 converts the public-exposure ledger into a six-gate checklist for future TRAPPIST-1 TTV/TTY timing sets. A candidate must declare timestamp provenance, exposure tier, public timing evidence, non-reuse of fitted timings, predeclared mode coverage, and final claim label. CDN-214 is reclassified as Tier B forecast-check-only: its observations and Agol forecast predate public GCFT, but the recovered Allen table path is post-boundary and b/d/e coverage completes zero predeclared modes. Clean TTY requires Tier A provenance, public residual testing, no fit reuse, and at least one complete mode among b-c-d, c-d-e, d-e-f, e-f-g, or f-g-h.