ci: right-size five single-core jobs to ubicloud-standard-2

actionlint, skill-docs, version-gate, pr-title-sync, and the evals report
job never exceed one core; standard-8 was ~4x the cost for zero wall-clock.
build-image and the eval matrix keep standard-8.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/pr-title-sync.yml

@@ -31,7 +31,7 @@ concurrency:
 jobs:
   sync:
     name: Sync PR title to VERSION
-    runs-on: ubicloud-standard-8
+    runs-on: ubicloud-standard-2
     permissions:
       contents: read
       pull-requests: write