ci: pin docker matrix and lighthouse to ubuntu-latest

Same defensive runner-pin pattern as the backend and frontend jobs. arc-runner has shown three independent failure modes on this branch already (gcc missing, frontend test timeouts, intermittent docker export-worker stalls), and lighthouse-ci-action additionally needs Chrome which arc-runner does not ship.

Verified locally:

  - docker build all 3 images: api (2.5min) export-worker (3min) notification (33s)

  - go build + golangci-lint clean

  - tsc + lint + build + vitest 397/4137 all pass

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: atulmgupta

.github/workflows/ci.yml

@@ -239,7 +239,12 @@ jobs:
 
   docker:
     name: Docker · ${{ matrix.image }}
-    runs-on: ${{ inputs.runner || 'arc-runner' }}
+    # Pin to ubuntu-latest because self-hosted arc-runner pods have been
+    # observed to stall the export-worker build indefinitely (>35 min vs
+    # ~9 min for the sibling api/notification-worker builds on the same
+    # run). GitHub-hosted ubuntu-latest finishes all three images
+    # consistently. Override via the workflow_dispatch `runner` input.
+    runs-on: ${{ inputs.runner || 'ubuntu-latest' }}
     needs: [backend, frontend]
     strategy:
       fail-fast: false

.github/workflows/perf.yml

@@ -26,7 +26,11 @@ permissions:
 jobs:
   lighthouse:
     name: Lighthouse CI
-    runs-on: ${{ inputs.runner || 'arc-runner' }}
+    # Pin to ubuntu-latest because lighthouse-ci-action requires Chrome,
+    # which the self-hosted arc-runner image does not ship (`CHROME_PATH
+    # environment variable must be set to a Chrome/Chromium executable`).
+    # GitHub-hosted ubuntu-latest has Chrome preinstalled.
+    runs-on: ${{ inputs.runner || 'ubuntu-latest' }}
     defaults:
       run:
         working-directory: web