[MNY-332] Dashboard: Checkout link error message improvements (#8550)

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## PR-Codex overview
This PR enhances error handling in the `billing.ts` files by checking for a specific error structure in the JSON response. If the error is present and formatted correctly, it returns a detailed error message instead of a generic one.

### Detailed summary
- Added error handling for JSON responses in `apps/dashboard/src/@/actions/billing.ts`:
  - Checks if `error` and `message` exist in the response.
  - Validates that `json.error.message` is a string.
  - Returns a structured error object with the message and status.

- Similar changes were made in `apps/dashboard/src/app/(app)/(stripe)/utils/billing.ts`.

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<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

## Bug Fixes
* Improved error message handling for billing operations to display API-provided error messages to users instead of generic fallback errors, enabling clearer feedback when checkout transactions encounter issues.

<sub>✏️ Tip: You can customize this high-level summary in your review settings.</sub>

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Author: MananTank

apps/dashboard/src/@/actions/billing.ts

@@ -109,6 +109,18 @@ export async function getChainInfraCheckoutURL(options: {
   }
 
   const json = await res.json();
+
+  if (
+    "error" in json &&
+    "message" in json.error &&
+    typeof json.error.message === "string"
+  ) {
+    return {
+      error: json.error.message,
+      status: "error",
+    } as const;
+  }
+
   if (!json.result) {
     return {
       error: "An unknown error occurred, please try again later.",

apps/dashboard/src/app/(app)/(stripe)/utils/billing.ts

@@ -75,6 +75,18 @@ export async function getBillingCheckoutUrl(options: {
   }
 
   const json = await res.json();
+
+  if (
+    "error" in json &&
+    "message" in json.error &&
+    typeof json.error.message === "string"
+  ) {
+    return {
+      error: json.error.message,
+      status: "error",
+    } as const;
+  }
+
   if (!json.result) {
     return {
       error: "An unknown error occurred, please try again later.",