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/primitive-sketchy.md

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+# Sketchy Filter (hand-drawn variant)
+
+Optional displacement filter that wobbles every stroke and edge slightly — turns any minimal variant into a hand-drawn "editorial" register without changing layout. Use when the diagram accompanies an essay rather than technical docs.
+
+## Grammar
+
+```svg
+<defs>
+  <filter id="sketchy" x="-2%" y="-2%" width="104%" height="104%">
+    <feTurbulence type="fractalNoise" baseFrequency="0.02" numOctaves="2" seed="4"/>
+    <feDisplacementMap in="SourceGraphic" scale="1.5"/>
+  </filter>
+</defs>
+
+<!-- Apply to a group wrapping shapes — NOT text -->
+<g filter="url(#sketchy)">
+  <!-- rects, paths, circles, lines go here -->
+</g>
+
+<!-- Text sits OUTSIDE the filtered group — legibility stays crisp -->
+<text ...>Labels go here</text>
+```
+
+## Tuning
+
+| Parameter | Range | Effect |
+|---|---|---|
+| `baseFrequency` | 0.01–0.04 | Lower = lazy wavy lines; higher = jittery. 0.02 default. |
+| `numOctaves` | 1–3 | More = more noise detail. 2 is plenty. |
+| `scale` | 1–6 | 1 barely-there, 1.5 default, 2 visible, 4+ cartoon. |
+| `seed` | integer | Swap for a different random pattern. |
+
+## Critical rule
+Filter shapes, NOT text. Displacement-mapped text becomes illegible. Structure your SVG so text is in a sibling group outside the filtered group.
+
+## When to use
+- Essay / blog post / newsletter where the diagram is the hero of a narrative page.
+- "Working sketch" register — showing something is mid-thought, not final architecture.
+
+## When not to use
+- Technical documentation (precision matters).
+- Diagrams with dense labels or tight alignments (filter reads as noise).
+- Dark variants — wobble reads as artifact on dark backgrounds. Test first.