normalizeResourceUrl mangles custom-scheme resource URLs (gitlab://x → https://gitlab://x)

## Description

`normalizeResourceUrl()` in `workshop-frontend/src/resourceMatching.ts` prepends `https://` to any resource URL that does not already start with `http(s)://`:

```ts
if (normalized && !/^https?:\/\//i.test(normalized)) {
normalized = 'https://' + normalized
}
```

Custom-vendor resources with their own schemes are first-class elsewhere in the platform — a blueprint's `gatekeeperName` + `typeUrlPattern` may reference any `GATEKEEPER_*` vendor, and `matchesResourceUrlPattern()` deliberately handles non-special schemes — but any custom-scheme URL passing through the blueprint flow gets mangled on the way to the backend: our `gitlab://inspekter-estate` reaches `account.getGatekeeperClassFor()` as `https://gitlab://inspekter-estate` (both via the auto-suggestion path and via `handleSaveActiveBinding`), and the UI displays the mangled form ("Using: https://gitlab://inspekter-estate").

Observed on our pinned build (`6478a144`) and still reproducing as of 2026-08-30; the regex is unchanged on current `main`.

## Steps observed

1. Deploy a custom gatekeeper whose vendor advertises a custom-scheme resource, e.g. `getSupportedResources()` → `{ urlPattern: "gitlab://*" }`.
2. Build a blueprint with a binding declaring `typeUrlPattern: "gitlab://*"`, `resourceUrl: "gitlab://inspekter-estate"`.
3. Import the blueprint and save the binding.
4. The vendor's `getGatekeeperClassFor()` receives `https://gitlab://inspekter-estate`; without a vendor-side workaround the bind fails (in our case: `This gatekeeper serves gitlab:// resources, not https://gitlab://inspekter-estate`), and the UI shows the mangled URL.

## Expected behavior

Prepend `https://` only when the URL has no scheme at all — e.g. test `/^[a-z][a-z0-9+.-]*:\/\//i` instead of `/^https?:\/\//i`.

## Workaround we use

Our vendors' `getGatekeeperClassFor()` strips a leading `https://` when it fronts the vendor's own scheme. That makes binding work, but the mangled form still persists in stored specs and in the UI, so it's tolerance rather than a fix.

Since the change looks like a one-line regex swap, we're happy to send it as a small PR per CONTRIBUTING.md if that's the direction you'd want — otherwise this is just the report.

Start in workshop-frontend/src/resourceMatching.ts at normalizeResourceUrl(), then inspect its use in the blueprint auto-suggestion and handleSaveActiveBinding flows. Change the scheme check so custom URLs such as gitlab://inspekter-estate are preserved while schemeless URLs still receive https://. Done means the backend and UI no longer receive or display the mangled https://gitlab:// form.

Written by the indexing model from the issue text.