trivial: add .cursor to gitignore (#1993)

<!--- Provide a general summary of your changes in the Title above -->

## Description

<!--- Describe your changes in detail -->

Used for Cursor-related configuration like cursor rules:
`.cursor/rules/example.mdc`

https://docs.cursor.com/context/rules-for-ai

## Related Issue(s)

- #N/A

## Verification

- [ ] **Your** code builds clean without any errors or warnings
- [ ] Manual testing done (required)
- [ ] Relevant automated test added (if you find this hard, leave it and
we'll help out)

## Documentation

- [ ] Documentation is updated (either in `docs`-directory, Altinnpedia
or a separate linked PR in
[altinn-studio-docs.](https://github.com/Altinn/altinn-studio-docs), if
applicable)

.gitignore

@@ -386,3 +386,6 @@ FodyWeavers.xsd
 **/.serviceowners-with-tokens.csv
 
 **/http-client.private.env.json
+
+# Cursor IDE related files
+.cursor