fix: sync delegated runners after allocation

[vincentkoc]

Summary

• refresh the coordinator external-runner portal after successful delegated warmup/run allocations
• add a regression test for Blacksmith JSON-list runner sync
• add a clearer Blacksmith outage hint that points users to coordinator-backed providers

Verification

• go test ./internal/cli -run 'TestSyncExternalRunnersBestEffortPostsBlacksmithJSONList|TestCoordinatorExternalRunnersFromBlacksmithListView' -count=1\n- go test ./internal/providers/blacksmith -run 'TestBlacksmithWarmupFailure|TestBlacksmithWarmupArgs' -count=1\n- git diff --check\n\n## Notes\n- Broad go test -timeout=30s ./internal/cli ./internal/providers/blacksmith timed out in unrelated TestInitProjectWritesExpectedFiles while waiting on git repo discovery; the targeted regressions above passed.