refactor(audience-sample): use SampleAppUi.Css references for inline CSS classes

AudienceSample.UI.cs RefreshStatusBar set status-cell classes via
inline strings ("state-warn", "state-ok", and "dim" five times) even
though SampleAppUi.Css.StateWarn / .StateOk / .Dim already exist for
exactly this purpose.

Migrates seven call sites to the constants. CSS-side renames now
need to touch one place (Css.Dim) instead of grep-and-replace across
the SetStatusCell call sites.

Per the user's "everything random goes in a constant" stance.

Follow-up to SDK-272 (centralisation of duplicated literals).

Author: ImmutableJeffrey

examples/audience/Assets/SampleApp/Scripts/AudienceSample.UI.cs

@@ -533,17 +533,17 @@ private void RefreshStatusBar()
             string? derivedFromKey = keyEmpty ? null : (isTest ? Constants.SandboxBaseUrl : Constants.ProductionBaseUrl);
             string? endpoint = hasOverride ? overrideUrl : derivedFromKey;
             bool warnState = hasOverride || (!keyEmpty && !isTest);
-            SetStatusCell(_statusEndpoint, endpoint, warnState ? "state-warn" : "state-ok");
+            SetStatusCell(_statusEndpoint, endpoint, warnState ? SampleAppUi.Css.StateWarn : SampleAppUi.Css.StateOk);
             _prodWarning.EnableInClassList(SampleAppUi.HiddenClass, hasOverride || keyEmpty || isTest);
 
             var consent = _initialised ? ImmutableAudience.CurrentConsent : ConsentOrder[Mathf.Clamp(_initialConsent?.index ?? 0, 0, ConsentOrder.Length - 1)];
             int cIdx = Array.IndexOf(ConsentOrder, consent);
-            SetStatusCell(_statusConsent, consent.ToLowercaseString(), cIdx >= 0 ? ConsentStateClass[cIdx] : "dim");
+            SetStatusCell(_statusConsent, consent.ToLowercaseString(), cIdx >= 0 ? ConsentStateClass[cIdx] : SampleAppUi.Css.Dim);
 
-            SetStatusCell(_statusAnon,    _initialised ? ImmutableAudience.AnonymousId : null, "dim");
-            SetStatusCell(_statusUser,    _initialised ? ImmutableAudience.UserId      : null, "dim");
-            SetStatusCell(_statusSession, _initialised ? ImmutableAudience.SessionId   : null, "dim");
-            SetStatusCell(_statusQueue,   _initialised ? ImmutableAudience.QueueSize.ToString(CultureInfo.InvariantCulture) : null, "dim");
+            SetStatusCell(_statusAnon,    _initialised ? ImmutableAudience.AnonymousId : null, SampleAppUi.Css.Dim);
+            SetStatusCell(_statusUser,    _initialised ? ImmutableAudience.UserId      : null, SampleAppUi.Css.Dim);
+            SetStatusCell(_statusSession, _initialised ? ImmutableAudience.SessionId   : null, SampleAppUi.Css.Dim);
+            SetStatusCell(_statusQueue,   _initialised ? ImmutableAudience.QueueSize.ToString(CultureInfo.InvariantCulture) : null, SampleAppUi.Css.Dim);
         }
 
         private void RefreshConsentPills()