v1.2.0

Dark mode: every artifact and the gallery index now ship a built-in light/dark toggle (fixed top-right, sun/moon).

• Follows the reader's OS by default. First open with no saved choice matches prefers-color-scheme; the toggle overrides and persists per-site in localStorage. With JavaScript off the page still follows the OS via a CSS media query and the (non-functional) toggle button stays hidden, so nothing is a dead control.
• Degrade-safe and print-safe. The base :root stays light and renders on any engine; the contrast-verified dark palette is emitted into two screen-scoped selectors (an explicit :root[data-theme="dark"] choice and the OS media query). Wrapping the dark tokens in @media screen keeps print-to-PDF light for clean handoff. A blocking head script applies a saved theme before first paint (no flash) and uses no .innerHTML, so the no-JS content contract is untouched.
• Dark palette. A cool, navy-biased set mirroring the light tokens one-for-one: elevation inverts (raised surfaces get lighter), the six severity triples are re-tuned for a dark ground, the code block gains a border so it does not melt into the page, and shadows drop their tint. All text pairings clear WCAG AA.
• Mermaid diagrams pick their palette at load from the resolved theme, so a diagram matches the page it opens in; a mid-session toggle re-themes diagrams on the next reload.
• Branding dark. A plain :root brand override still styles light only; to brand dark, append a :root[data-theme="dark"] override. SKILL.md and references/patterns.md updated: the scaffold is no longer described as light-only.