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-flowchart.md

@@ -0,0 +1,23 @@
+# Flowchart
+
+**Best for:** decision logic, algorithms, user-facing branching flows ("Should I…?"), onboarding routing, support-triage trees.
+
+## Layout conventions
+- Shape carries type, not color:
+  - **Oval** (`rx=20`) — start / end
+  - **Rectangle** (`rx=6`) — step / action
+  - **Diamond** — decision (≤3 exits)
+  - **Small filled ink dot** (`r=4`) — merge point where branches rejoin
+- Flow runs top→down. From a diamond, conventional exits: Yes to the right, No below — but label every outgoing arrow regardless.
+- Use coral on the happy path *or* on the single most consequential decision — never on every decision.
+- If two arrows must cross, use a small arc jump on one so the crossing is readable.
+
+## Anti-patterns
+- Using fill color to signal node type (shape does that).
+- Decision diamond with 4+ exits — refactor into nested diamonds.
+- Unlabeled decision branches.
+
+## Examples
+- `assets/example-flowchart.html` — minimal light
+- `assets/example-flowchart-dark.html` — minimal dark
+- `assets/example-flowchart-full.html` — full editorial