fix: choose route for initial URL imports

[SingLinkNetwork]

What changed

• First-time manual URL imports now explicitly offer Sync via proxy and Sync directly.
• Proxy remains selected by default, so existing privacy and routing behavior is unchanged.
• The selected route is passed to the existing profile download API.
• Adds widget coverage for default proxy and explicit direct selection.

Root cause

The download layer already supported direct routing, but the first-import dialog always called it with the proxy default and offered no route choice.

Verification

• Static diff check and independent code review passed.
• Local Flutter is unavailable, so widget rendering/tests were not claimed as run locally.
• Full cross-platform GitHub Actions is required before merge.

Closes #110