[feature request] add protection against duplicate link

[braboobssiere]

currently it will only failed if slugs are duplicated, but it allowed long url to be duplicated if the slugs are different

it would be more intuitive to returned old short link if user input duplicated long link

[github-actions]

👋 Here's some info that may help:

🔗 Related issues:

• Duplicate links #15 — Duplicate links (closed): This feature was previously requested. The maintainer decided not to implement it, explaining:

"It's reasonable for a link to be able to create multiple short links; we won't consider this feature for now"

The rationale was that having multiple short links pointing to the same URL is intentional — it allows tracking analytics per link, e.g., sharing the same URL in different campaigns or channels.

📖 From docs: No documentation covers duplicate link prevention. The existing behavior (slugs must be unique, URLs can repeat) is by design.

Hope this helps! Feel free to provide more details if these don't address your case.

[braboobssiere]

for that reason, do you considered to add it as a setting at least? (one of the set env) because while it make sense for tracking it could become redundant if the service open to public