fix(05-03): parse session response before passing to updateSessionInfo

CRITICAL BUG:
- refreshCurrentSessionRest passed raw Response object to updateSessionInfo
- Should parse with response.json() first
- Caused two major issues:

ISSUE 1: Redux Serialization Error
- Response object dispatched to Redux (non-serializable)
- Error: "A non-serializable value was detected in an action"

ISSUE 2: Backing Tracks Never Extracted
- updateSessionInfo received Response instead of parsed data
- response.participants was undefined (Response has no participants property)
- Backing track extraction code never ran
- mixerHelper.backingTracks stayed empty

SOLUTION:
Parse response before passing to updateSessionInfo:
  const response = await getSession(currentSessionIdRef.current);
  const data = await response.json();  // ← ADDED
  updateSessionInfo(data, callback, force);

Now data.participants exists and backing tracks are extracted correctly.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/src/hooks/useSessionModel.js

@@ -734,7 +734,8 @@ export default function useSessionModel(app, server, sessionScreen) {
 
     try {
       const response = await getSession(currentSessionIdRef.current);
-      updateSessionInfo(response, callback, force);
+      const data = await response.json();
+      updateSessionInfo(data, callback, force);
     } catch (jqXHR) {
       if (jqXHR.status !== 404) {
         app.notifyServerError(jqXHR, "Unable to refresh session data");