chore: Rename LICENSE.md to LICENSE for better compatibility with Bazel tooling (#3950)

Starting with aspect_rules_js 3.x, the default npm packaging behavior
excludes Markdown files (for example, *.md) from generated package
contents.

As a result, packages that ship their license exclusively as
LICENSE.md are no longer picked up by Bazel-based license collection
pipelines.

This affects downstream consumers such as Gerrit Code Review, which
relies on Bazel tooling to aggregate third-party licenses from
node_modules. In this setup, marked was the only dependency whose
license was omitted, because it was provided solely as LICENSE.md.

Rename the file to LICENSE so the package license is preserved in
Bazel-generated npm package directories and can be detected by license
aggregation and compliance tooling.

This is a packaging-only change and does not affect runtime behavior.

Fixes #3949
Refs: aspect-build/rules_js#2806