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/commands/bd-init.md

@@ -0,0 +1,14 @@
+---
+description: Initialize beads in the current project
+---
+
+Initialize beads issue tracking in the current directory.
+
+Use the beads MCP `init` tool to set up a new beads database.
+
+After initialization:
+1. Show the database location
+2. Explain the basic workflow (or suggest running `/bd-workflow`)
+3. Suggest creating the first issue with `/bd-create`
+
+If beads is already initialized, inform the user and show project stats using the `stats` tool.