403 errors show an unfriendly "Network Response 403" message

## Description

When the database or proxy returns a 403 Forbidden, the user sees the generic `Network Response 403` title with whatever raw message the server returns, which is often an opaque JSON blob or empty. There is no dedicated branch in `createDisplayError` for 403, so it falls through to the catch-all `NetworkError` path.

A 403 can be caused by several things (credentials, permissions, proxy configuration), so the message should stay generic and point the user at what they can reasonably check.

## Environment

- All environments, browser-based

## Steps to Reproduce

1. Connect to a database or proxy that will reject requests with 403
2. Trigger any request (e.g. schema sync)

## Expected Behavior

A friendly, generic message such as:

> **Access denied**
> The server refused this request. Check that your connection credentials and permissions are correct, then try again.

## Actual Behavior

Title says "Network Response 403" and the message is either the raw server response or the generic "An error occurred. Please try again."

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Start at the createDisplayError entry point and trace how a 403 reaches the catch-all NetworkError path. Reproduce a rejected request during a schema sync or similar browser request, then verify that 403 responses show a generic access-denied message rather than the raw server response or network title.

Written by the indexing model from the issue text.