perf(traffic): skip unchanged global writes between heartbeats (#6931)

* perf(traffic): skip unchanged global writes between heartbeats

Persist directional usage changes immediately, including lower resets, while
refreshing identical global totals only at an inclusive one-hour heartbeat.
Use the GORM clock consistently for the existing 24-hour freshness window and
preserve local-only snapshots, quota enforcement, and downstream forwarding.

Fixes #6928

* docs(traffic): describe persisted global heartbeat timestamps

Replace the stale every-push model comment with the change-or-hourly-heartbeat
rule. Keep the local-counter separation, delta accounting, MAX fold and reset
semantics explicit without treating UpdatedAt as a last-push timestamp.

Address the nonblocking review feedback on PR #6931 without rewriting
published history.

Refs #6928

.github/workflows/ci.yml

@@ -80,6 +80,16 @@ jobs:
             exit 1
           fi
 
+      - name: PostgreSQL global-traffic heartbeat regressions
+        run: |
+          set -o pipefail
+          go test ./internal/web/service -run '^TestGlobalTrafficHeartbeatPostgres$' -count=1 -v | tee /tmp/postgres-global-traffic-heartbeat.log
+          passed=$(grep -c -- '^--- PASS' /tmp/postgres-global-traffic-heartbeat.log || true)
+          if [ "$passed" -ne 1 ]; then
+            echo "expected 1 passing global-traffic heartbeat test, got $passed" >&2
+            exit 1
+          fi
+
       - name: PostgreSQL deferred-commit test
         run: |
           set -o pipefail