feat(design): promote the offline notebook's design iteration into the reference

Five promotions from the offline-readiness notebook, landing its design iteration in the token layer, the chrome, and the pattern set so every consumer starts from these defaults.

• Corrects four token-layer contrast failures; every corrected pairing measures 4.59:1 or better in both themes.
• Replaces the lab TOC chip row with a semantic vertical ordered list; pages still carrying chip markup render as plain vertical lists.
• Self-hosts the chrome fonts (Inter, JetBrains Mono, IBM Plex, each with its OFL license); the chrome makes only same-origin requests.
• Adds the disclosure-index pattern with its class contract: CSS selectors follow the generator's derived collection names.
• Adds an authoring page carrying three composition rulings: one shared content width, root-level text orients while disclosures carry detail, and enumerations are real lists.

The consumer de-override in lab/offline-readiness follows after this deploys.