Initial release: diagram-design v1.0

Thirteen editorial diagram types (architecture, flowchart, sequence,
state, ER, timeline, swimlane, quadrant, nested, tree, layers, venn,
pyramid) as self-contained HTML files with inline SVG.

Progressive disclosure: lean SKILL.md points to per-type references.
Neutral stone+rust default skin, first-run gate that prompts users
to customize the style guide from their own website, URL-based
onboarding, annotation-callout primitive, sketchy filter variant,
live gallery at assets/index.html.

references/type-architecture.md

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+# Architecture
+
+**Best for:** system overviews, data-flow diagrams, integration maps, infra topology.
+
+## Layout conventions
+- Group components by tier or trust boundary (frontend → backend → data; public → private).
+- Primary flow runs left→right or top→down. Pick one and hold it.
+- Draw arrows before boxes so z-order puts connections behind components.
+- 1–2 coral focal nodes: the primary integration point, the primary data store, or the key decision node.
+- Dashed boundary rectangles mark regions (VPC, security group, trust zone); labels sit on a paper-colored mask over the boundary line.
+
+## Anti-patterns
+- Every box in coral ("this is important too") — hierarchy collapses.
+- Bidirectional arrow when one direction is obvious from context.
+- Legend floating inside the diagram area.
+
+## Examples
+- `assets/example-architecture.html` — minimal light
+- `assets/example-architecture-dark.html` — minimal dark
+- `assets/example-architecture-full.html` — full editorial