Fix SVG/PNG export to exclude selection decorations

[sn3ha-dev278]

Summary:

Fixes an issue where selected diagram elements were included in exported SVG and PNG files.
Closes #1318.

Description for the changelog:

Remove selection highlights from exported SVG and PNG diagrams.

Declaration:

Thanks for submitting a pull request, please make sure:

• content meets the license for this project
• appropriate unit tests have been created / modified
• functional tests created / modified for changes in functionality
• you have read the contribution guide and agree to the Code of Conduct
• any use of AI has been declared in this pull request

Other info:

[jgadsden]

Hello @sn3ha-dev278 , thanks for submitting the pull request
please answer the following:

• appropriate unit tests have been created / modified
• functional tests created / modified for changes in functionality if required
• any use of AI

[jgadsden]

tested with and without time-out delays, both work OK and no race condition detected
@sn3ha-dev278 this is an identical solution to one that used AI to provide the solution, can you confirm whether you used generative AI or not?

[sn3ha-dev278]

Thanks for the review.
1)Unit tests: I didn’t add new unit tests since this change only affects client-side export rendering and doesn’t touch core logic or data models.
2)Functional tests: No automated functional tests were added. I verified the fix manually by exporting PNG and SVG diagrams with selected elements and confirming that selection highlights no longer appear in the exports.
3)Use of AI: Generative AI was used for general guidance. However, I reviewed, understood, and manually tested before submitting.

[jgadsden]

OK, thanks for the testing and clarification @sn3ha-dev278