fix: check response.ok before parsing JSON in fetch calls

Fix JSON parsing errors when server returns non-JSON responses:
- Check response.ok before calling response.json()
- Add fallback error messages using status text
- Apply fix to all fetch calls across 12 components

This prevents 'JSON.parse: unexpected character' errors when
server returns HTML error pages or other non-JSON responses.

src/app/admin/users/components/EditUserForm.tsx

@@ -35,10 +35,16 @@ export default function EditUserForm({ user, availablePlayers }: EditUserFormPro
         body: JSON.stringify(formData),
       })
 
-      const data = await response.json()
-
       if (!response.ok) {
-        throw new Error(data.error || "Failed to update user")
+        try {
+          const errorData = await response.json()
+          throw new Error(errorData.error || "Failed to update user")
+        } catch (jsonError) {
+          if (jsonError instanceof Error && jsonError.message !== "Failed to update user") {
+            throw jsonError
+          }
+          throw new Error(`Failed to update user: ${response.status} ${response.statusText}`)
+        }
       }
 
       setSuccess("User updated successfully!")