Improve schema_apply error handling and add credentials

- Add better JSON parsing with error logging
- Add credentials: same-origin to ensure session cookies are sent
- Show helpful error message when server returns invalid response

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

webapp/settings.php

@@ -1321,9 +1321,18 @@ async function applySchemaUpdates() {
                 "Content-Type": "application/json",
                 "X-CSRF-Token": CSRF_TOKEN
             },
+            credentials: "same-origin",
             body: JSON.stringify({ csrf_token: CSRF_TOKEN })
         });
-        const data = await response.json();
+
+        const text = await response.text();
+        let data;
+        try {
+            data = JSON.parse(text);
+        } catch (parseError) {
+            console.error("Failed to parse response:", text);
+            throw new Error("Server returned invalid response. Check error logs.");
+        }
 
         if (!data.success) {
             throw new Error(data.error || "Failed to apply schema changes");