feat: Add Claude Code plugin for beads [addresses #28]

Adds a Claude Code plugin for one-command installation of beads via
/plugin command. The plugin bundles the MCP server, slash commands,
and an autonomous task agent.

Components:
- Plugin metadata with MCP server configuration
- 8 slash commands for core workflow (/bd-ready, /bd-create, etc.)
- Task agent for autonomous execution (@task-agent)
- Comprehensive plugin documentation (PLUGIN.md)

The plugin provides a lower-friction installation path for Claude Code
users who want integrated slash commands rather than direct MCP tools.

Related: https://github.com/steveyegge/beads/issues/28

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

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

.claude-plugin/plugin.json

@@ -0,0 +1,37 @@
+{
+  "name": "beads",
+  "description": "AI-supervised issue tracker for coding workflows. Manage tasks, discover work, and maintain context with simple CLI commands.",
+  "version": "0.9.0",
+  "author": {
+    "name": "Steve Yegge",
+    "url": "https://github.com/steveyegge"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/steveyegge/beads"
+  },
+  "license": "MIT",
+  "homepage": "https://github.com/steveyegge/beads",
+  "keywords": [
+    "issue-tracker",
+    "task-management",
+    "ai-workflow",
+    "agent-memory",
+    "mcp-server"
+  ],
+  "mcpServers": {
+    "beads": {
+      "command": "uv",
+      "args": [
+        "--directory",
+        "${CLAUDE_PLUGIN_ROOT}/integrations/beads-mcp",
+        "run",
+        "beads-mcp"
+      ],
+      "env": {
+        "BEADS_PATH": "bd",
+        "BEADS_ACTOR": "${USER}"
+      }
+    }
+  }
+}