ci: enable SSE for wait-for-hydra in PR validation (#243)

Use the hydra-github-bridge SSE endpoint for real-time build status
detection instead of polling the GitHub API. Reduces wait time from
minutes (poll interval) to seconds (event-driven).

Tested end-to-end in PR #241 — all validation jobs passed.

Author: angerman

.github/workflows/pr-validate.yml

@@ -18,6 +18,7 @@ jobs:
     - uses: input-output-hk/actions/wait-for-hydra@latest
       with:
         check: required
+        hydra-status-url: https://ci.zw3rk.com
 
   discover:
     needs: wait-for-hydra