Foundation: notebook style, plotting theme, and run-mode header #67

Goal

Make sixty notebooks look like one book, in the TypeSafe palette, and make each one say which mode it ran in.

Scope

• A matplotlib style using the palette: pink #F386A1, ink #1E1E1E, magenta #E551BA, panel grey #DEDEDE, paper #FEFEFE, with a categorical order and a sequential ramp that stay readable for colour-blind readers.
• Chart helpers for the recurring figures: confusion matrix, probability bars for one answer, threshold sweep, risk and coverage curve.
• A run_header() helper that prints the recipe number and title, the backend mode, and, in a synthetic run, the sentence that metrics are pipeline checks and not Jev results.
• A small helper to display one typed answer readably.

Acceptance criteria

• Example figures are rendered in the pull request description
• Charts are legible on GitHub's light and dark notebook views
• Tests cover the header text for each mode
• Lint and tests pass in CI, or locally with the output pasted in the pull request if CI does not exist yet

Dependencies

• Blocked by Foundation: project scaffolding and Python package skeleton #61 (project scaffolding and Python package skeleton)
• Unblocks Foundation: recipe template and scaffolder #68
• Tracked in Epic: Foundation #74

References

• Recipe contract
• Catalog
• TypeSafe documentation index for tools: https://docs.typesafe.ai/llms.txt
• Python SDK: https://docs.typesafe.ai/sdk/python