test(audience): add ci marker test that stamps run metadata on CDP (SDK-317)

- New [UnityTest] AudienceCiTestMarker_EmitsRunMetadata. Skips
  outside CI (AUDIENCE_TEST_RUN_ID and AUDIENCE_TEST_CELL_ID both
  unset). Inside CI, calls LoadAndInit then emits one
  ImmutableAudience.Track("audience_ci_test_marker", { source: "ci",
  ciRunId, ciCellId }).
- Lets dashboards filter test traffic in / out:
  - select event_name = "audience_ci_test_marker" lists every CI run
    that hit CDP, with run / cell metadata directly on the row.
  - properties.buildGuid on the marker matches the buildGuid the SDK
    auto-emits on every game_launch event from the same cell binary,
    so a follow-up filter pulls the rest of the cell's events.
- Standalone test rather than a hook in LoadAndInit so the marker
  stays explicit and opt-in. Other tests do not silently emit a
  side-event; the SampleApp and SDK carry no CI / QA-specific
  knowledge.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ImmutableJeffrey

examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppLiveFireTests.cs

@@ -128,6 +128,30 @@ private IEnumerator SetConsentVia(string consentButtonName)
 
         // ---- Tests ----
 
+        // Marks this as coming from CI.
+        [UnityTest]
+        public IEnumerator AudienceCiTestMarker_EmitsRunMetadata()
+        {
+            var runId  = Environment.GetEnvironmentVariable("AUDIENCE_TEST_RUN_ID");
+            var cellId = Environment.GetEnvironmentVariable("AUDIENCE_TEST_CELL_ID");
+            if (string.IsNullOrEmpty(runId) && string.IsNullOrEmpty(cellId))
+            {
+                Assert.Ignore("Not running in CI.");
+                yield break;
+            }
+
+            yield return LoadAndInit();
+
+            ImmutableAudience.Track("audience_ci_test_marker", new System.Collections.Generic.Dictionary<string, object>
+            {
+                ["source"]   = "ci",
+                ["ciRunId"]  = runId  ?? string.Empty,
+                ["ciCellId"] = cellId ?? string.Empty,
+            });
+
+            yield return null;
+        }
+
         [UnityTest]
         public IEnumerator InitTrackFlush_AgainstSandbox_FlushReportsOk()
         {