fix: make SonarCloud scan non-blocking with continue-on-error

SonarCloud returns 404 — project may need first-run setup on
sonarcloud.io. Tests and coverage should not be blocked by this.
Will investigate SonarCloud setup separately.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: abhizipstack

.github/workflows/core-backend-tests.yaml

@@ -61,6 +61,7 @@ jobs:
       - name: SonarCloud Scan
         uses: SonarSource/sonarcloud-github-action@master
         if: ${{ github.actor != 'dependabot[bot]' }}
+        continue-on-error: true
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}