refactor: move Claude Code plugin to dedicated subdirectory (GH#985)

Move all plugin content to claude-plugin/ subdirectory for cleaner
separation from core beads functionality:

- claude-plugin/.claude-plugin/plugin.json - plugin manifest
- claude-plugin/commands/ - all slash commands
- claude-plugin/agents/ - task-agent (now in correct location)
- claude-plugin/skills/beads/ - beads skill with resources

Root .claude-plugin/ now only contains marketplace.json pointing
to ./claude-plugin.

Note: After updating, users may need to clear plugin cache:
  rm -rf ~/.claude/plugins/cache/beads-marketplace/

Fixes #985

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

Executed-By: beads/crew/dave
Rig: beads
Role: crew

.claude-plugin/agents/task-agent.md

@@ -1,60 +0,0 @@
----
-description: Autonomous agent that finds and completes ready tasks
----
-
-You are a task-completion agent for beads. Your goal is to find ready work and complete it autonomously.
-
-# Agent Workflow
-
-1. **Find Ready Work**
-   - Use the `ready` MCP tool to get unblocked tasks
-   - Prefer higher priority tasks (P0 > P1 > P2 > P3 > P4)
-   - If no ready tasks, report completion
-
-2. **Claim the Task**
-   - Use the `show` tool to get full task details
-   - Use the `update` tool to set status to `in_progress`
-   - Report what you're working on
-
-3. **Execute the Task**
-   - Read the task description carefully
-   - Use available tools to complete the work
-   - Follow best practices from project documentation
-   - Run tests if applicable
-
-4. **Track Discoveries**
-   - If you find bugs, TODOs, or related work:
-     - Use `create` tool to file new issues
-     - Use `dep` tool with `discovered-from` to link them
-   - This maintains context for future work
-
-5. **Complete the Task**
-   - Verify the work is done correctly
-   - Use `close` tool with a clear completion message
-   - Report what was accomplished
-
-6. **Continue**
-   - Check for newly unblocked work with `ready`
-   - Repeat the cycle
-
-# Important Guidelines
-
-- Always update issue status (`in_progress` when starting, close when done)
-- Link discovered work with `discovered-from` dependencies
-- Don't close issues unless work is actually complete
-- If blocked, use `update` to set status to `blocked` and explain why
-- Communicate clearly about progress and blockers
-
-# Available Tools
-
-Via beads MCP server:
-- `ready` - Find unblocked tasks
-- `show` - Get task details
-- `update` - Update task status/fields
-- `create` - Create new issues
-- `dep` - Manage dependencies
-- `close` - Complete tasks
-- `blocked` - Check blocked issues
-- `stats` - View project stats
-
-You are autonomous but should communicate your progress clearly. Start by finding ready work!

.claude-plugin/marketplace.json

@@ -7,7 +7,7 @@
   "plugins": [
     {
       "name": "beads",
-      "source": "./",
+      "source": "./claude-plugin",
       "description": "AI-supervised issue tracker for coding workflows",
       "version": "0.46.0"
     }

.claude-plugin/plugin.json

@@ -1,42 +0,0 @@
-{
-  "name": "beads",
-  "description": "AI-supervised issue tracker for coding workflows. Manage tasks, discover work, and maintain context with simple CLI commands.",
-  "version": "0.46.0",
-  "author": {
-    "name": "Steve Yegge",
-    "url": "https://github.com/steveyegge"
-  },
-  "repository": "https://github.com/steveyegge/beads",
-  "license": "MIT",
-  "homepage": "https://github.com/steveyegge/beads",
-  "keywords": [
-    "issue-tracker",
-    "task-management",
-    "ai-workflow",
-    "agent-memory"
-  ],
-  "hooks": {
-    "SessionStart": [
-      {
-        "matcher": "",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "bd prime"
-          }
-        ]
-      }
-    ],
-    "PreCompact": [
-      {
-        "matcher": "",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "bd prime"
-          }
-        ]
-      }
-    ]
-  }
-}