v2.12.2 — per-role scene policy + anchor=vocabulary docs

Patch fixing the 'same scene on every slide' anti-pattern when style anchor bakes in a fixed setting. Builder now injects a per-role scene policy directive that overrides scene leakage on non-hook slides. Hook keeps the literal scene; framework/data/steps/comparison/myth-vs-truth get clean textured fields with content dominating; quote/cta allow one minimal decorative element. Docs: _universal-rules.md §0 (anchor=vocabulary) + §11 (scene policy table); dark-academia.md rewritten as model vocabulary anchor; SKILL.md anti-pattern constraint.