Parameter promotion gate: review registries before changing code defaults

[maxcharvey]

Priority: P2 — process gate, applies across submodules.

registries/parameters.yml (CharvBrain wiki) holds scoped model priors. Before hardcoding or changing any default in code (brc_mod TAU_MIN/TAU_MAX/FRAC_PERM/A_PARTICLE, optics k values, emission fractions), each candidate value must have source, scope, contradiction status, and model_ready reviewed.

Rule: only promote default or explicitly approved regime-specific values; use registries/parameters.yml + registries/model_decisions.yml as the pre-implementation checklist.

Ref: wiki problems.md ISSUE-004.