📝 Update mqt-cc reference (#1773)

## Description

This PR updates the `mqt-cc` reference to include a link to the
published version.

## Checklist

- [x] The pull request only contains commits that are focused and
relevant to this change.
- [x] ~~I have added appropriate tests that cover the new/changed
functionality.~~
- [x] I have updated the documentation to reflect these changes.
- [x] ~~I have added entries to the changelog for any noteworthy
additions, changes, fixes, or removals.~~
- [x] ~~I have added migration instructions to the upgrade guide (if
needed).~~
- [x] The changes follow the project's style guidelines and introduce no
new warnings.
- [x] The changes are fully tested and pass the CI checks.
- [x] I have reviewed my own code changes.

Author: denialhaag

README.md

@@ -148,6 +148,7 @@ When citing the compilation framework built on MLIR, cite the MQT Compiler Colle
   author       = {Burgholzer, Lukas and Haag, Daniel and Stade, Yannick and Rovara, Damian and Hopf, Patrick and Wille, Robert},
   year         = {2026},
   booktitle    = {Design, Automation and Test in Europe},
+  doi          = {10.23919/DATE69613.2026.11539504},
   eprint       = {2604.08674},
   eprinttype   = {arxiv},
 }

docs/references.md

@@ -36,6 +36,7 @@ If you want to cite the MQT Compiler Collection, please use the following BibTeX
   author       = {Burgholzer, Lukas and Haag, Daniel and Stade, Yannick and Rovara, Damian and Hopf, Patrick and Wille, Robert},
   year         = {2026},
   booktitle    = {Design, Automation and Test in Europe},
+  doi          = {10.23919/DATE69613.2026.11539504},
   eprint       = {2604.08674},
   eprinttype   = {arxiv},
 }

docs/refs.bib

@@ -228,6 +228,7 @@ @inproceedings{MQTCompilerCollection2026
   author              = {Burgholzer, Lukas and Haag, Daniel and Stade, Yannick and Rovara, Damian and Hopf, Patrick and Wille, Robert},
   year                = {2026},
   booktitle           = date,
+  doi                 = {10.23919/DATE69613.2026.11539504},
   eprint              = {2604.08674},
   eprinttype          = {arxiv},
 }