Add plugin manifest and documentation for agents/workflows

- Add .claude-plugin/plugin.json for potential plugin distribution
- Add agents/README.md explaining agent file purpose and usage
- Add workflows/README.md clarifying that workflows are design docs,
  not executable automation (Claude Code doesn't natively execute YAML)

This improves documentation and enables potential future portability
as a plugin.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/plugin.json

@@ -0,0 +1,17 @@
+{
+  "name": "will-homelab",
+  "version": "1.0.0",
+  "description": "Personal assistant and multi-agent system for homelab management, including Gmail, Calendar, Kubernetes, and Linux administration",
+  "author": {
+    "name": "Will"
+  },
+  "license": "MIT",
+  "keywords": [
+    "personal-assistant",
+    "homelab",
+    "kubernetes",
+    "gmail",
+    "calendar",
+    "linux"
+  ]
+}