* docs: Add DESIGN.md specification for Langflow's visual design system
Machine-readable design tokens (YAML frontmatter) paired with
human-readable design rationale following the open-source DESIGN.md
format from Google Labs. Intended for AI agents generating UI that
must match Langflow's visual identity.
Covers 129 color tokens, 15 typography scales, 50 component
definitions, spacing/rounding/elevation systems, dark mode strategy,
and the 14-hue data type color system used for node port encoding.
* ci: Add DESIGN.md lint workflow
Runs `@google/design.md lint` against DESIGN.md on pull requests that
modify the file. Catches spec violations, broken token references, and
WCAG AA contrast failures before merge. CLI version is pinned via env
var so format spec changes require a deliberate bump.
* ci: Integrate DESIGN.md lint into CI Success pipeline
Replaces the standalone workflow with a job inside ci.yml so it gates
the "CI Success" aggregate check. Path-filter skips the job on PRs
that don't touch DESIGN.md, so cost is near-zero for normal PRs.
