Prevent unsafe defaults in the Investor Signals recipe

[georgeatparallel]

Why I think these changes should land

These three cases can cause real harm even when the happy path works:

• A fresh checkout silently used the sample fund list. Running the monitor setup could therefore create paid monitors for funds the user never chose.
• CSV downloads put the shared demo passphrase in the URL, where it could appear in browser history and request logs.
• When a company had no domain, the Attio lookup used a name substring and trusted the first result. That could attach the wrong CRM record and change the signal's priority.

What changed

• Monitor creation and the initial sweep now stop with a clear setup message until the user provides a real watchlist. Other commands such as list and cancel still work.
• CSV exports now use the existing authenticated request header and download the response in the browser. Query-string authentication is no longer accepted.
• Attio matching now requires a domain. If there is no reliable identity, the recipe reports the CRM check as unavailable instead of guessing.

Validation

• 61 backend tests passed
• 10 frontend tests passed
• Ruff passed
• TypeScript and Vite production build passed
• pip check passed
• git diff --check passed

Stacked on parallel-web#53 at ed6fa29.