Don't auto-load Web Workflow on bare localhost

[makermelissa-piclaw]

Problem

Visiting the editor at bare http://localhost/ (i.e. running it locally for development with no ?backend= and no ?host= URL params) silently auto-selects the Web Workflow. WebWorkflow.parseParams() then sees isTestHost() is true with no host= supplied and returns:

You are connected with localhost, but didn't supply the device hostname.

The user never reaches the connect dialog, so they can't pick BLE / Serial / USB instead.

Cause

getBackend() in js/script.js falls through to Web Workflow whenever isLocal() is true:

} else if (isLocal()) {
    return getBackendWorkflow("web");
}

isLocal() returns true for bare localhost (no path constraint on the localhost branch), so Web Workflow is auto-loaded even when there's no plausible Web Workflow target.

Fix

Only auto-pick Web Workflow when there's actually a target for it:

• an mdns hostname (*.local)
• an IP-address hostname
• or an explicit host= URL param

Otherwise return null so script.js falls through to the connect dialog and lets the user choose.

} else if (isLocal()) {
    if (isMdns() || isIp() || getUrlParam("host", false)) {
        return getBackendWorkflow("web");
    }
}

Risk / compatibility

Small surface change. The only behaviour difference is on bare localhost with no URL hints — previously it auto-picked Web Workflow (and immediately errored), now it falls through to the connect dialog. Any URL that previously connected successfully (mdns, IP, or ?host=) still does.

Testing

Verified locally on a dev server: bare http://localhost:PORT/ now shows the connect dialog instead of the "didn't supply the device hostname" error, and BLE / Serial / USB selections work as expected. Web Workflow paths (mdns / IP / ?host=) unchanged.