fix(cli): add missing memu-server CLI entry point

[Crpdim]

📝 Pull Request Summary

Please provide a short summary explaining the purpose of this PR.

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✅ What does this PR do?

• Creates the missing src/memu/server/ package with CLI implementation
• Implements memu-server entry point with start, info, --help, and --version commands
• Adds tests/test_server_cli.py for test coverage
• The start command currently shows a helpful message directing users to programmatic API usage

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🤔 Why is this change needed?

The pyproject.toml defines a console script entry point memu-server = "memu.server.cli:main", but the memu.server module doesn't exist. This causes ModuleNotFoundError when users install the package and try to run memu-server. Fixes #354.

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🔍 Type of Change

Please check what applies:

• Bug fix
• New feature
• Documentation update
• Refactor / cleanup
• Other (please explain)

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✅ PR Quality Checklist

• PR title follows the conventional format (feat:, fix:, docs:)
• Changes are limited in scope and easy to review
• Documentation updated where applicable
• No breaking changes (or clearly documented)
• Related issues or discussions linked

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📌 Optional

• Screenshots or examples added (if applicable)
• Edge cases considered
• Follow-up tasks mentioned