Dashboard: Fix Import Contract Modal submit button loading state (#7970)

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## PR-Codex overview
This PR updates the conditional rendering logic in the `modal.tsx` file to use the `form.formState.isSubmitting` state instead of `addContractToProject.isPending`. This change ensures that the button reflects the correct submission state during the import process.

### Detailed summary
- Changed the conditional check for displaying the loading spinner from `addContractToProject.isPending` to `form.formState.isSubmitting`.
- Updated the button text from "Importing" to reflect the new state condition.

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

## Summary by CodeRabbit

* **Bug Fixes**
  * Import Contract modal: The submit button now accurately reflects the submission state. It shows a spinner and the label changes to “Importing” while the form is submitting, and reverts to the standard icon with “Import” when idle. This improves user feedback, reduces confusion, and helps prevent duplicate submissions by clearly indicating when an import is in progress.

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Author: MananTank

apps/dashboard/src/@/components/contracts/import-contract/modal.tsx

@@ -231,13 +231,13 @@ function ImportForm(props: {
             </Button>
           ) : (
             <Button className="gap-2" type="submit">
-              {addContractToProject.isPending ? (
+              {form.formState.isSubmitting ? (
                 <Spinner className="size-4" />
               ) : (
                 <ArrowDownToLineIcon className="size-4" />
               )}
 
-              {addContractToProject.isPending ? "Importing" : "Import"}
+              {form.formState.isSubmitting ? "Importing" : "Import"}
             </Button>
           )}
         </div>