fix(input): reject non-OK HTTP responses when reading from a URL

[schani]

Bug

When quicktype reads JSON/JSON Schema input from a URL (--src http://...)
and the server returns an HTTP error status (e.g. a 401 caused by an expired
auth token passed via --http-header), quicktype did not report an error.
Instead it silently treated the error response body as legitimate input:

• If the error body happened to be valid JSON, quicktype generated types
  from it and exited 0.
• If it wasn't valid JSON, quicktype emitted a misleading "Syntax error in
  input JSON" with no indication the real cause was an HTTP failure.

Root cause

In packages/quicktype-core/src/input/io/NodeIO.ts,
readableFromFileOrURL called globalThis.fetch() and passed
response.body straight to the parser with no response.ok / status check:

const response = await globalThis.fetch(fileOrURL, {
    headers: parseHeaders(httpHeaders),
});

return readableFromResponseBody(defined(response.body));

Fix

Check response.ok right after the fetch call and throw a clear error
(including the HTTP status) when the response is not OK, instead of handing
the error body to the parser:

if (!response.ok) {
    throw new Error(`HTTP ${response.status} ${response.statusText}`);
}

Test coverage

Added a unit test in test/unit/url-input.test.ts (this bug is Node-only
HTTP-fetch behavior that the JSON/JSON Schema fixture-test machinery has no
mechanism to exercise, since fixtures drive file-based input, not an HTTP
server): the local test server now returns HTTP 401 with a JSON body for
unauthorized.json, and a new test asserts readFromFileOrURL rejects with
an error containing HTTP 401 Unauthorized instead of resolving.

Verification

• Confirmed the bug on unfixed master: a local server returning HTTP 401
  with a JSON body caused node dist/index.js --lang typescript --src http://localhost:8473/data.json --just-types to print a bogus TypeScript
  interface derived from the error body and exit 0.
• After the fix, the same repro now fails as expected:

  Error: Cannot read from file or URL http://localhost:8473/data.json: Error: HTTP 401 Unauthorized.
  

  with exit code 1.
• npm run build passes.
• npx vitest run test/unit/url-input.test.ts passes (3/3, including the
  new test).
• Full CI (broader fixture suite) will validate the rest.

Fixes #2572

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