Add Claude Code plugin + marketplace manifests

Adds .claude-plugin/plugin.json and .claude-plugin/marketplace.json so the repo can be installed via /plugin marketplace add. Uses "skills": ["./"] so the existing root SKILL.md is picked up without relocation — standalone install path is unchanged. Also removes stray Cocoon AI author reference from SKILL.md frontmatter.

.claude-plugin/marketplace.json

@@ -0,0 +1,15 @@
+{
+  "name": "diagram-design",
+  "metadata": {
+    "description": "Editorial-quality technical and product diagrams — 13 types rendered as standalone HTML with inline SVG, skinnable to match your brand"
+  },
+  "owner": {
+    "name": "Cathryn Lavery"
+  },
+  "plugins": [
+    {
+      "name": "diagram-design",
+      "source": "./"
+    }
+  ]
+}

.claude-plugin/plugin.json

@@ -0,0 +1,17 @@
+{
+  "name": "diagram-design",
+  "description": "Editorial-quality technical and product diagrams — 13 types rendered as standalone HTML with inline SVG, skinnable to match your brand",
+  "version": "1.0.0",
+  "homepage": "https://github.com/cathrynlavery/diagram-design",
+  "repository": "https://github.com/cathrynlavery/diagram-design",
+  "license": "MIT",
+  "keywords": [
+    "diagrams",
+    "svg",
+    "architecture",
+    "flowchart",
+    "visualization",
+    "editorial"
+  ],
+  "skills": ["./"]
+}

README.md

@@ -57,6 +57,18 @@ ln -s ~/code/diagram-design ~/.claude/skills/diagram-design
 
 Restart Claude Code. The skill registers as `diagram-design` and activates whenever you ask Claude to make a diagram.
 
+### Alternative: install as a plugin
+
+Quicker to install — but the skill lives in the plugin cache, so edits to `references/style-guide.md` don't survive plugin updates. Pick this if you just want to try it out; use the clone route above if you plan to customize the style guide by hand.
+
+**Claude Code:**
+```
+/plugin marketplace add cathrynlavery/diagram-design
+/plugin install diagram-design@diagram-design
+```
+
+**Claude Cowork:** Customize → Directory → Plugins → **+** → paste `cathrynlavery/diagram-design` → Sync, then install from the Personal list.
+
 ---
 
 ## Onboarding — make it look like *your* brand

SKILL.md

@@ -4,7 +4,6 @@ description: Create technical and product diagrams — architecture, flowchart,
 license: MIT
 metadata:
   version: "1.0"
-  author: Cocoon AI (hello@cocoon-ai.com)
 ---
 
 # Diagram Design