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-timeline.md

@@ -0,0 +1,20 @@
+# Timeline
+
+**Best for:** release history, project milestones, incident timelines, roadmaps, changelog visualizations.
+
+## Layout conventions
+- Horizontal hairline baseline across the middle (`stroke-width=1`).
+- Tick marks at time boundaries (quarters, months, sprints) with date labels below in Geist Mono.
+- Events: small filled circles (`r=4`) on the baseline. Labels alternate above and below to prevent collision, connected to the circle with a 1px hairline drop.
+- Major milestones: coral circle (`r=6`) + bold Geist label.
+- Time scale must be honest: if intervals are non-equal, space the circles non-equally. Don't fake linear spacing for aesthetics. Break the axis visibly if a region is too dense.
+
+## Anti-patterns
+- Equal-spacing events that aren't equally spaced in time.
+- Missing axis labels ("what unit is this?").
+- Crowded labels without vertical offset — illegible.
+
+## Examples
+- `assets/example-timeline.html` — minimal light
+- `assets/example-timeline-dark.html` — minimal dark
+- `assets/example-timeline-full.html` — full editorial