fix: remove delete account button and direct users to support (#8515)

## Summary
Reverts PR #5216 delete account functionality. The delete button only
removed Firebase accounts without canceling Stripe subscriptions,
causing orphaned accounts and support issues.

## Changes
- Removed delete account button from UserPanel.vue
- Added text directing users to contact support@comfy.org for account
deletion (clickable mailto: link)
- Cleaned up related code: removed `handleDeleteAccount` from
useCurrentUser.ts, `deleteAccount` from useFirebaseAuthActions.ts,
`_deleteAccount` from firebaseAuthStore.ts
- Updated en/main.json locale with `contactSupport` key using {email}
placeholder

## Testing
- Typecheck and lint pass
- Manual verification: user settings panel shows contact support text
instead of delete button

## Related Issues
Fixes COM-14243

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8515-fix-remove-delete-account-button-and-direct-users-to-support-2fa6d73d3650819dbc83efb41c07a809)
by [Unito](https://www.unito.io)

Co-authored-by: Amp <amp@ampcode.com>

src/locales/en/main.json

@@ -1949,13 +1949,7 @@
       "auth/cancelled-popup-request": "Sign-in was cancelled. Please try again."
     },
     "deleteAccount": {
-      "deleteAccount": "Delete Account",
-      "confirmTitle": "Delete Account",
-      "confirmMessage": "Are you sure you want to delete your account? This action cannot be undone and will permanently remove all your data.",
-      "confirm": "Delete Account",
-      "cancel": "Cancel",
-      "success": "Account Deleted",
-      "successDetail": "Your account has been successfully deleted."
+      "contactSupport": "To delete your account, please contact {email}"
     },
     "reauthRequired": {
       "title": "Re-authentication Required",