chore: fix JavaScript lint errors (issue #15944)

[AnujNayak108]

Resolves #15944.

Description

What is the purpose of this pull request?

This pull request:

• Fixes JavaScript linting failures in @stdlib/_tools/licenses/update-header.
• Updates @example code snippets in lib/main.js and lib/index.js to use @stdlib/_tools/licenses/header-regexp helper headerRegExp( 'Apache-2.0', 'js' ) instead of a literal regex containing /\/\// to prevent slash escaping conflicts during ESLint doctest string replacements.
• Concatenates '/* @license Apache-2.0 *' + '/' in @example code blocks to prevent premature termination of the outer JSDoc comment.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• Fix JavaScript lint errors #15944

Questions

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No.

Other

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No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

I consulted an AI assistant to analyze the internal ESLint doctest error traceback and understand the root cause. All changes were tested and verified locally using make lint-javascript-files and unit tests.

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