#16704: Signal: reduce REST lock contention in send/receive loop

## Summary This PR reduces Signal latency and lock contention when using `signal-cli-rest-api`, then hardens CI around the follow-up test fixes. ## What Changed - Signal runtime - prioritize outbound sends over receive polling under contention - reduce probe/account-check pressure in hot paths - account-aware probe behavior and health-check dedupe - tune health refresh cadence to reduce unnecessary load - UI / config conflict resolution - resolved gateway URL and app-gateway merge-conflict fallout cleanly - CI stability - stabilize macOS TS test pool selection (`vmForks` disabled on macOS CI) - fix PR changed-scope base detection to use merge-base from current base branch head ## Validation - GitHub Actions run: https://github.com/openclaw/openclaw/actions/runs/22210247043 - Required checks are green; `macos` is correctly skipped for this PR scope. ## Notes - No private credentials, tokens, or personal identifiers were added.