chore(config): ignore local mcp.json and add example template

[Code-MonkeyZhang]

PR Description

This PR makes mcp.json a user-local configuration file and provides a committed template for reference.

Why

mcp.json can contain user-specific MCP server settings and API keys. Keeping it in the repo risks leaking secrets and makes local customization harder. A tracked example file plus a gitignored real config is a safer, clearer workflow.

What changed

• .gitignore: added mcp.json so user configs aren’t committed.
• mini_agent/config/mcp-example.json: added as the canonical MCP config template.
• mini_agent/config/mcp.json: removed from version control (users should create their own).
• Setup scripts: now download mcp-example.json from GitHub and save it as mcp.json in the user config directory: scripts/setup-config.sh & scripts/setup-config.ps1
• Examples/tests default to the template file to avoid depending on a gitignored local file:
  examples/04_full_agent.py
tests/test_mcp.py
tests/test_integration.py
• Docs/templates updated to explain the new flow and that MCP is optional:
  README.md
README_CN.md
mini_agent/config/config-example.yaml

How to use MCP now

Copy mini_agent/config/mcp-example.json to mini_agent/config/mcp.json, edit it to enable servers and add keys. If mcp.json is missing, Mini Agent still runs but without MCP tools.

Testing
All test passed

=================================================== warnings summary ====================================================
mini_agent/acp/__init__.py:12
mini_agent/acp/__init__.py:12
  /Users/zhangyufeng/WorkSpace/CodePlace/Personal-Project/Projec Chris/MiniAgent/Mini-Agent-Original/mini_agent/acp/__init__.py:12: DeprecationWarning: Using `AgentSideConnection` directly is deprecated, please use `acp.run_agent` instead.
    from acp import (

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
================================= 92 passed, 3 skipped, 2 warnings in 115.04s (0:01:55) =================================
(mini-agent) (base) zhangyufeng@zhangyufengdeMacBook-Air Mini-Agent-Original %