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-quadrant.md

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+# Quadrant
+
+**Best for:** prioritization (Impact × Effort), positioning (Reach × Frequency), portfolio maps, 2×2 decision frames.
+
+## Layout conventions
+- 2×2 grid. Axis lines: 1px ink cross through the center.
+- Axis labels at the *ends* of each axis (e.g., `HIGH IMPACT →` on the right, `LOW IMPACT ←` on the left — Geist Mono eyebrow). Never label at the midpoint.
+- Items: small labeled dots (`r=4`) positioned in the quadrants. Labels 8–10px away; don't let labels cross axis lines.
+- Coral on the "do first" item (typically top-right).
+- Limit to ~12 items; cluster or split beyond that.
+
+## Anti-patterns
+- Four filled quadrants in different colors — position + label does the work; color noise weakens it.
+- Items placed on axis lines (ambiguous quadrant).
+- Missing axis names.
+
+## Examples
+- `assets/example-quadrant.html` — minimal light
+- `assets/example-quadrant-dark.html` — minimal dark
+- `assets/example-quadrant-full.html` — full editorial