feat(mcp): add restart all MCP servers functionality

[Timorleiderman]

Summary

• Add ability to restart all MCP servers without restarting opencode
• Useful for developers working on MCP servers who need to quickly reconnect after code changes

Changes

• Add MCP.restartAll() function to disconnect and reconnect all connected/failed servers
• Add POST /mcp/restart API endpoint
• Add r keybind in MCP dialog to restart all servers
• Add /restart-mcp slash command
• Add "Restart MCPs" to command palette
• Regenerate SDK with new endpoint

Usage

1. Open MCP dialog with /mcp, then press r to restart all
2. Use /restart-mcp slash command
3. Use command palette → "Restart MCPs"