Add Claude Code plugin and marketplace config

Enables Claude Code users to install with:
  /plugin marketplace add microsoft/Build-CLI
  /plugin install microsoft-events@microsoft-events-marketplace

Follows the MicrosoftDocs/mcp pattern for Claude plugin packaging.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: pdebruin

.claude-plugin/marketplace.json

@@ -0,0 +1,13 @@
+{
+  "name": "microsoft-events-marketplace",
+  "owner": {
+    "name": "Microsoft"
+  },
+  "plugins": [
+    {
+      "name": "microsoft-events",
+      "source": "./",
+      "description": "Connect your project to Microsoft Build and Ignite sessions — discover relevant talks, explore what's new for your stack, and plan next steps from your development environment."
+    }
+  ]
+}

.claude-plugin/plugin.json

@@ -0,0 +1,14 @@
+{
+  "name": "microsoft-events",
+  "description": "Connect your project to Microsoft Build and Ignite sessions — discover relevant talks, explore what's new for your stack, and plan next steps from your development environment.",
+  "version": "1.0.0",
+  "author": {
+    "name": "Microsoft"
+  },
+  "homepage": "https://github.com/microsoft/Build-CLI",
+  "repository": "https://github.com/microsoft/Build-CLI",
+  "keywords": ["microsoft", "build", "ignite", "events", "sessions", "learn"],
+  "license": "Apache-2.0",
+  "skills": "./skills/",
+  "mcpServers": "./.mcp.json"
+}