Replace the gear spinner with the thinking-orbs canvas engine (vendored
framework-free build, driven by js/orb.js in the "solving" state) and the
inline SVG brand icon with a pure CSS book whose cover flips open on page
load and while the brand is hovered (js/logo.js).
Static frontend with vendored marked/DOMPurify, bounded Markdown
pipeline, same-origin mock server with scenario selection, unit,
contract and CDP end-to-end tests under frontend/**.
