v1.6: fix HIGH security vuln — remove plaintext cookie backup

- Remove KEY_COOKIES_BACKUP plaintext fallback from PreferencesManager
- getCookies() now fails closed (force re-login) if EncryptedSharedPreferences unavailable
- Set android:allowBackup="false" to prevent adb backup extraction of session data
- Add missing gradle-wrapper.jar to repo

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/build.gradle.kts

@@ -11,8 +11,8 @@ android {
         applicationId = "me.khodak.claudeusage"
         minSdk = 26
         targetSdk = 34
-        versionCode = 6
-        versionName = "1.5"
+        versionCode = 7
+        versionName = "1.6"
     }
 
     signingConfigs {