Guard CDP probe ports against low-port/discard values

When DevTools CDP endpoint is auto-detected (GetPropW 'wkappbot.cdp' or --remote-debugging-port= regex), the resulting port can be 0/9/low-privileged leftover from stale/corrupted props. Probing 127.0.0.1:<low> throws HttpRequestException that cascades into any caller path (slack send/list, suggest, etc) and surfaces in RunMain top-level catch as a crash report.

Steps