Fix Pro users seeing upgrade prompts

Pro users were incorrectly seeing payment prompts because BillingManager
initialization would return early when enabled=false, skipping the Pro
flavor check. This left billingPreferences=null, causing hasPurchased()
to return false.

Moved Pro flavor handling before the enabled check to ensure Pro users
always get ads removed regardless of billing manager state.

Fixes user reports of "app keeps trying to force another payment" in Pro version.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: TomTasche

app/src/main/java/at/tomtasche/reader/nonfree/BillingManager.java

@@ -16,18 +16,18 @@ public class BillingManager {
     public void initialize(Context context, AnalyticsManager analyticsManager, AdManager adManager) {
         this.adManager = adManager;
 
+        // Handle Pro flavor first, regardless of enabled state
+        if (BuildConfig.FLAVOR.equals("pro")) {
+            adManager.removeAds();
+            return;
+        }
+
         if (!enabled) {
             adManager.showGoogleAds();
-
             return;
         }
 
         billingPreferences = new BillingPreferences(context);
-
-        if (BuildConfig.FLAVOR.equals("pro")) {
-            billingPreferences.setPurchased(true);
-        }
-
         enforceAds();
     }