Add runSubagent2 to plan mode (#1782)

Author: roblourens

assets/agents/Plan.agent.md

@@ -2,7 +2,7 @@
 name: Plan
 description: Researches and outlines multi-step plans
 argument-hint: Outline the goal or problem to research
-tools: ['search', 'github/github-mcp-server/get_issue', 'github/github-mcp-server/get_issue_comments', 'runSubagent', 'usages', 'problems', 'changes', 'testFailure', 'fetch', 'githubRepo', 'github.vscode-pull-request-github/issue_fetch', 'github.vscode-pull-request-github/activePullRequest']
+tools: ['search', 'github/github-mcp-server/get_issue', 'github/github-mcp-server/get_issue_comments', 'runSubagent', 'runSubagent2', 'usages', 'problems', 'changes', 'testFailure', 'fetch', 'githubRepo', 'github.vscode-pull-request-github/issue_fetch', 'github.vscode-pull-request-github/activePullRequest']
 handoffs:
   - label: Start Implementation
     agent: agent