Add MCPManager to coordinate multiple MCP client connections and route
tool calls to the appropriate server.
MCPManager (server/mcp_manager.go):
- Manages connections to multiple MCP servers simultaneously
- Routes tool calls to appropriate server by tool name
- Parallel tool execution with configurable concurrency
- Tool result caching with TTL and size limits
- Aggregates tools from all connected servers
- Server config validation (name, command, args, env)
Relates to #7865
code4me2