fix examples

[boxbag]

Fixes a variety of problems in examples found during testing

1. Indentation in mcp_hello_world was incorrect, causing the example to not run after client is instantiated
2. References to saqadri local filesystem in mcp_basic_slack_agent, mcp_model_selector, workflow_evaluator_optimizer`
3. mcp_basic_slack requires path to folder on local filesystem, similar to other examples
4. mcp_researcher could not resolve relative path ./agent_folder. Had to pass the full path using os.path.abspath. Also need to create the agent_folder directory if it doesn't exist on local filesystem

Example error from mcp_basic_slack

Error accessing directory /Users/saqadri/Desktop: Error: ENOENT: no such file or 
directory, stat '/Users/saqadri/Desktop'
    at async Object.stat (node:internal/fs/promises:1037:18)
    at async file:///Users/bochen/.npm/_npx/a3241bba59c344f5/node_modules/@modelcontextprotocol/server-filesystem/dist/index.js:33:23
    at async Promise.all (index 0)
    at async file:///Users/bochen/.npm/_npx/a3241bba59c344f5/node_modules/@modelcontextprotocol/server-filesystem/dist/index.js:31:1 {
  errno: -2,
  code: 'ENOENT',
  syscall: 'stat',
  path: '/Users/saqadri/Desktop'
}

Example error from mcp_researcher

{"level":"INFO","timestamp":"2025-03-31T13:21:05.308384","namespace":"mcp_agent.mcp.stdio.mcpserver.stderr","message":"docker: Error response from daemon: create ./agent_folder: \"./agent_folder\" includes invalid characters for a local volume name, only \"[a-zA-Z0-9][a-zA-Z0-9_.-]\" are allowed. If you intended to pass a host directory, use absolute path.\nSee 'docker run --help'."}

[saqadri]

🥹 🙏🏼 @boxbag keep the fixes coming!