Port analyze/diff tools from figma-use, split tools into domain files
Analyze: colors, typography, spacing, clusters
Diff: diff_create (tree diff), diff_show (preview changes)
Utility: get_components, get_current_page, arrange, node_to_component
Split schema.ts (2600 lines) into read, create, modify, structure,
variables, vector, analyze, registry — each under 600 lines.
Clean up inline types (use Color, Vector, SceneNode from existing defs).
Update AGENTS.md and CONTRIBUTING.md with code quality guidelines.
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