docs: add lychee config cleanup note for lint:links adopters

[zeitlinger]

Summary

Add a "Lychee config cleanup" section to the lint:links docs listing which lychee.toml entries can be removed when adopting flint, because flint handles them at runtime via --remap.

Motivation: When adopting flint in opentelemetry-java-instrumentation#16270, I initially kept (and even added) lychee config entries that flint already handles — the existing docs explain what flint does but don't explicitly tell adopters what they can remove from their lychee config.

Entries documented for removal

• GitHub blob remap workaround for lychee#1729
• #issuecomment-* excludes
• #L\d+ line-number anchor excludes

[Copilot]

Pull request overview

This PR adds a "Lychee config cleanup" section to the lint:links documentation to help adopters understand which lychee.toml configuration entries they can safely remove when adopting flint. The documentation clarifies that flint handles certain URL patterns (GitHub blob remaps, issue comment anchors, and line-number anchors) at runtime via --remap arguments, eliminating the need for these configurations in the lychee config file.

Changes:

• Adds a "Lychee config cleanup" subsection explaining which lychee.toml entries can be removed
• Documents three specific patterns that flint handles: GitHub blob remap for lychee#1729, #issuecomment-* excludes, and #L\d+ line-number excludes
• Includes a note explaining why flint uses --remap instead of --exclude

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