Qobuz: Fix authentication and add automatic credential fetching

Qobuz API now requires intent=stream parameter for stream URL requests,
and the app_secret must be extracted using the Spoofbuz decoding method
from bundle.js rather than plain-text values.

Changes:
- Add intent=stream parameter to stream URL requests
- Add QobuzCredentialFetcher class to extract credentials from web player
- Add "Fetch Credentials" button to Qobuz settings page
- Decode obfuscated app secrets using seed/timezone/info/extras method

This fixes "Invalid Request Signature" errors that prevented playback.

src/settings/qobuzsettingspage.ui

@@ -115,6 +115,16 @@
         </property>
        </widget>
       </item>
+      <item row="3" column="1">
+       <widget class="QPushButton" name="button_fetch_credentials">
+        <property name="text">
+         <string>Fetch Credentials</string>
+        </property>
+        <property name="toolTip">
+         <string>Automatically fetch app ID and secret from Qobuz web player</string>
+        </property>
+       </widget>
+      </item>
      </layout>
     </widget>
    </item>