fix: billingPlan when applying credits

Ensure applying:

1. credits when on Free org will upgrade org to Pro
2. regular credits when on Pro org will leave plan unchanged
3. regular credits when on Scale or above org will leave plan unchanged
4. startup credits when on Free org will upgrade org to Scale

src/routes/(console)/apply-credit/+page.svelte

@@ -77,7 +77,7 @@
     $: selectedOrgId = tempOrgId;
 
     function isUpgrade() {
-        const newPlan = page.data.plansInfo.get(billingPlan);
+        const newPlan = $plansInfo.get(billingPlan);
         return currentPlan && newPlan && currentPlan.order < newPlan.order;
     }
 
@@ -227,24 +227,22 @@
     function getBillingPlan(): Tier | undefined {
         const campaignPlan =
             campaign?.plan && $plansInfo.get(campaign.plan) ? $plansInfo.get(campaign.plan) : null;
-        const orgPlan =
-            selectedOrg?.billingPlan && $plansInfo.get(selectedOrg.billingPlan)
-                ? $plansInfo.get(selectedOrg.billingPlan)
-                : null;
+        const newPlan = $plansInfo.get(billingPlan);
 
-        if (!campaignPlan && !orgPlan) {
-            return;
+        // if campaign has a plan and it's higher than the selected new plan
+        if (campaignPlan?.order > newPlan?.order) {
+            return campaignPlan.$id as Tier;
         }
-        if (!campaignPlan) {
-            return selectedOrg?.billingPlan;
+
+        // if current plan's order is higher than the selected new plan
+        if (currentPlan?.order > newPlan?.order) {
+            return currentPlan.$id as Tier;
         }
-        if (!orgPlan) {
-            return campaign.plan;
-        }
-        return campaignPlan.order > orgPlan.order ? campaign.plan : selectedOrg?.billingPlan;
+
+        return billingPlan;
     }
 
-    $: if (selectedOrg) {
+    $: if (currentPlan) {
         billingPlan = getBillingPlan();
     }