v0.14.0 — themed decks (deterministic design)

build_doc pptx specs gain an optional theme — {bg, accent, ink, muted, panel, rail, page_numbers, font} — plus design layouts stat / quote / comparison. A designed deck (deep-navy + orange, accent rail, page numbers, 16:9, type hierarchy) is now ONE deterministic call with zero model usage. Without theme, legacy template layouts are unchanged.