[Release] 5.1.2

[dpfaffenbauer]

Patch release of the 5.1 line.

• Classic Admin: the "About CoreShop" menu entry works again and Studio-only menu entries are hidden ([Classic Admin] "About CoreShop" menu entry does nothing #3236, [Classic Admin] Wire the "About CoreShop" menu entry to the classic resource dispatcher #3237).
• Docs: demo links point at the CoreShop 5 demo ([Docs] Point the demo links at the CoreShop 5 demo #3234), Elasticsearch client configuration key fixed ([Docs] Fix Elasticsearch client configuration key and link client bundles (5.1) #3239).
• Includes the 5.0 upmerge ([UPMERGE] 5.0 -> 5.1 #3244).

Version::RELEASE_VERSION → 2; adds the ## 5.1.2 changelog section. After the merge: tag 5.1.2 on the resulting build commit and publish the GitHub release with generated notes, as for 5.1.1.

[coreshop-bot]

🚦 PR Guardrail

⚠️ Advisory mode: this PR is not blocked (yet). Once the guardrail is switched to enforce: true, the points below would be violations.

❌ R8 — Release milestone

The release PR for 5.1.2 has no milestone.

➡️ Assign the milestone 5.1.2 to the PR (create it first if it does not exist yet). The milestone is closed with the release.

❌ R5 — CI

Failed checks on the current head: add-to-project / add-to-project.

➡️ Fix the failed checks and push the fix. The guardrail re-evaluates automatically once CI completes.

ℹ️ Some CI checks are still running. The CI result is re-evaluated automatically once they finish.

_{Automated comment by the PR guardrail — details and FAQ: docs/GUARDRAILS.md in coreshop/workflow-collection.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud