fix(ci): add always-reporting CI Gate so fork PRs stop deadlocking

The validate/build/test/compose-parity jobs are gated to trusted author
associations so untrusted fork code never runs on the self-hosted runners.
But a job skipped via a job-level if reports no status, and branch protection
requires the job names typecheck/lint/format/build/test directly, so fork PRs
hang on 'Expected - waiting for status to be reported' and can never merge.

Add a single CI Gate job (if: always(), needs the gated jobs, no checkout so it
runs no third-party code) that fails only when a gated job actually
failed/cancelled and passes when they succeed or skip-for-fork. Branch
protection should require CI Gate instead of the individual job names.

Closes #1461

.github/workflows/ci.yml

@@ -160,3 +160,37 @@ jobs:
 
       - name: Assert compose parity (compose.yaml vs docker-compose.integrated.yml)
         run: bash tests/docker/compose-parity.sh
+
+  # Single always-reporting status that branch protection requires.
+  #
+  # The validate/build/test jobs are gated to trusted author associations so
+  # untrusted fork code never executes on the self-hosted runners. A job skipped
+  # by a job-level `if` reports no status, so requiring those job names directly
+  # leaves fork PRs stuck on "Expected - waiting for status to be reported"
+  # forever. Requiring this gate instead keeps the contract satisfiable:
+  #   - trusted PR: gate is green only if every gated job actually succeeded
+  #   - fork PR:    gated jobs skip, gate reports green so the PR is mergeable
+  #                 (fork code is still reviewed by a maintainer before merge)
+  #
+  # No checkout here: the gate only inspects upstream job results, so it runs no
+  # third-party code and is safe on the self-hosted runner.
+  ci-gate:
+    if: always()
+    needs: [validate, build, test]
+    runs-on: [self-hosted, linux, x64]
+    name: CI Gate
+    steps:
+      - name: Verify gated jobs did not fail
+        env:
+          VALIDATE: ${{ needs.validate.result }}
+          BUILD: ${{ needs.build.result }}
+          TEST: ${{ needs.test.result }}
+        run: |
+          echo "validate=$VALIDATE build=$BUILD test=$TEST"
+          for result in "$VALIDATE" "$BUILD" "$TEST"; do
+            if [ "$result" = "failure" ] || [ "$result" = "cancelled" ]; then
+              echo "[X] A required CI job did not pass (result: $result)"
+              exit 1
+            fi
+          done
+          echo "[OK] CI gate satisfied (success or skipped-for-fork)"