Split the single flowchart.mmd into flowchart/platform-overview.mmd
(all 5 phases) and flowchart/round-lifecycle.mmd (round/draw detail),
plus render-pdf.sh to generate print-ready A4/A3 PDFs with a consistent
theme, header/footer, and legible contrast against the page background.
Also flip the operational policy in CLAUDE.md: the app now always runs
via Docker (dev and prod alike), with the venv reserved for tests,
migration authoring, and one-time secret/key-generation scripts.
