fix(cli): support ui5mcp help flag

[sh962214-hub]

Summary

• allow ui5mcp --help and ui5mcp -h to print usage and exit successfully
• keep the existing no-argument server startup behavior unchanged
• keep unexpected arguments rejected with exit code 2

Validation

• npm run unit -- test/lib/cli.ts
• npm run build-test
• npm run build
• npm run lint -- --quiet src/cli.ts test/lib/cli.ts
• node .\bin\ui5mcp.js --help

[cla-assistant]

All committers have signed the CLA.

[RandomByte]

Thank you for your interest in contributing to this project. I noticed this PR appears to have been created by an AI bot.

Before we can review and consider this contribution, we need to clarify a few things:

CLA Requirement: All contributions to SAP open source projects require signing our Contributor License Agreement (CLA). A CLA is a legal agreement that requires legal capacity to enter into — something an AI bot cannot do on its own. Therefore, we need a human or legal entity to take responsibility for this contribution and sign the CLA.

Human Review: Our guidelines for AI-generated code contributions place obligations on contributors to review AI-generated output for compliance with licensing terms, third-party IP considerations, and tool-specific filtering requirements. These responsibilities require human judgment and accountability.

Could you please clarify:

1. Is there a human maintainer or organization behind this bot who can review this contribution, take responsibility for its content, and sign the CLA?
2. Has a human reviewed this PR for compliance with the project's license and our AI contribution guidelines?

Without a human in the loop who can sign the CLA and assume responsibility for the contribution, we unfortunately cannot accept this PR.