ci: fix staging smoke test port — read STAGING_GO_HTTP_PORT, not hardcoded 82 (#854)

## Problem
The "Deploy Staging" job's Smoke Test always fails with `Staging
/api/stats did not return engine field`.

Root cause: the step hardcodes `http://localhost:82/api/stats`, but
`docker-compose.staging.yml:21` publishes the container on
`${STAGING_GO_HTTP_PORT:-80}:80`. Default is port 80, not 82. curl gets
ECONNREFUSED, `-sf` swallows the error, `grep -q engine` sees empty
input → failure.

Verified on staging VM: `ss -lntp` shows only `:80` listening; `docker
ps` confirms `0.0.0.0:80->80/tcp`. A `curl http://localhost:82` returns
connection-refused.

## Fix
Read `STAGING_GO_HTTP_PORT` (same default as compose) so the smoke test
tracks the port the container was actually launched on. Failure message
now includes the resolved port to make future port mismatches
self-diagnosing.

## Tested
Logic only — the curl + grep pattern is unchanged. If any CI env
override sets `STAGING_GO_HTTP_PORT`, the smoke test now follows it.

Co-authored-by: Kpa-clawbot <agent@corescope.local>

.github/workflows/deploy.yml

@@ -432,10 +432,11 @@ jobs:
 
       - name: Smoke test staging API
         run: |
-          if curl -sf http://localhost:82/api/stats | grep -q engine; then
+          PORT="${STAGING_GO_HTTP_PORT:-80}"
+          if curl -sf "http://localhost:${PORT}/api/stats" | grep -q engine; then
             echo "Staging verified — engine field present ✅"
           else
-            echo "Staging /api/stats did not return engine field"
+            echo "Staging /api/stats did not return engine field (port ${PORT})"
             exit 1
           fi