feat: add download_examples command

[Ki-Seki]

Description

Summary: Create unified CLI endpoints and add a download examples command. Now we have two commands available as below.

memoryos-py3.10(base) ➜  MemOS git:(Ki-Seki/issue52) ✗ memos --help                          
usage: memos [-h] {download_examples,export_openapi} ...

MemOS Command Line Interface

positional arguments:
  {download_examples,export_openapi}
                        Available commands
    download_examples   Download example files
    export_openapi      Export OpenAPI schema to JSON file

options:
  -h, --help            show this help message and exit

Fix: #52

Reviewer: @J1awei-Yang

Checklist:

• I have performed a self-review of my own code | 我已自行检查了自己的代码
• I have commented my code in hard-to-understand areas | 我已在难以理解的地方对代码进行了注释
• I have added tests that prove my fix is effective or that my feature works | 我已添加测试以证明我的修复有效或功能正常
• I have added necessary documentation (if applicable) | 我已添加必要的文档（如果适用）
• I have linked the issue to this PR (if applicable) | 我已将 issue 链接到此 PR（如果适用）
• I have mentioned the person who will review this PR | 我已提及将审查此 PR 的人

[Copilot]

Pull Request Overview

Adds a unified CLI entry point under memos and introduces a new download_examples command alongside the existing export_openapi functionality.

• Implements download_examples in src/memos/cli.py and updates tests accordingly
• Removes the standalone scripts/export_openapi.py and registers the memos script in pyproject.toml
• Updates documentation and Makefile to reflect the new CLI usage

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/test_cli.py	Added tests for download_examples and export_openapi commands
src/memos/cli.py	Implemented new download_examples command and centralized CLI
scripts/export_openapi.py	Removed legacy standalone export script
pyproject.toml	Registered memos entry point under Poetry scripts
README.md	Added documentation for download_examples command
Makefile	Updated openapi target to use memos export_openapi

Comments suppressed due to low confidence (3)

src/memos/cli.py:33

• The docstring in download_examples is placed after the import statement, so it won't be recognized as the function's docstring. Move it immediately after the def download_examples line to properly document the function.

    """Download examples from the MemOS repository."""

tests/test_cli.py:67

• This test checks the return value but doesn't verify that directories and files are actually created. Consider adding assertions on os.makedirs and open calls (or on the extracted_files list) to fully cover the extraction logic.

        assert result is True

README.md:177

• The README documents the download_examples command but doesn’t include an example for export_openapi. Adding a brief usage snippet for memos export_openapi --output <path> will keep the CLI documentation complete.

#### Download Examples