ci(mutation): make Stryker report upload best-effort (refs #62)

The Gitea artifact backend returns 500 to actions/upload-artifact@v3 (server-side,
distinct from the @v4 GHES guard). With if: always() that 500 failed the whole
mutation job even though the ratchet passed — red on main and on every PR. Mark the
three report uploads continue-on-error: true so the mutation *gate* stays the Stryker
ratchet (make mutation's exit code), not the report upload. Documented in
gitea-actions-gotchas.md §4.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -51,25 +51,30 @@ jobs:
         with:
           dotnet-version: '10.0.x'
       - run: make mutation
-      # Publish the Stryker HTML report. `if: always()` uploads it even when the
+      # Publish the Stryker HTML reports. `if: always()` uploads them even when the
       # ratchet fails — that is exactly when you want to inspect the survivors.
-      # Glob handles Stryker's non-deterministic StrykerOutput/<timestamp>/ dir.
-      # Pinned to @v3 deliberately: @v4 refuses to run on Gitea (GHES guard) —
-      # see docs/runbooks/gitea-actions-gotchas.md §4.
+      # `continue-on-error` keeps the upload best-effort: the mutation *gate* is the
+      # ratchet (make mutation's exit code), not the report, so a Gitea artifact-backend
+      # 500 must not fail the job (gitea-actions-gotchas.md §4). Glob handles Stryker's
+      # non-deterministic StrykerOutput/<timestamp>/ dir. Pinned @v3: @v4's bundled
+      # @actions/artifact hard-aborts on non-github.com (GHES guard) — see the runbook.
       - uses: https://github.com/actions/upload-artifact@v3
         if: always()
+        continue-on-error: true
         with:
           name: acl-mutation-report
           path: services/acl/StrykerOutput/**/reports/mutation-report.html
           if-no-files-found: warn
       - uses: https://github.com/actions/upload-artifact@v3
         if: always()
+        continue-on-error: true
         with:
           name: event-subscriber-mutation-report
           path: services/event-subscriber/StrykerOutput/**/reports/mutation-report.html
           if-no-files-found: warn
       - uses: https://github.com/actions/upload-artifact@v3
         if: always()
+        continue-on-error: true
         with:
           name: domain-mutation-report
           path: services/domain/StrykerOutput/**/reports/mutation-report.html