Refactor JumpIn logic to reuse UI2 component and remove modal behavior

[braianj]

Context

Currently, the logic for handling JumpIn (launcher detection, modal display, and redirects) is duplicated in both repositories:

• jump-site
• ui2

This duplication increases maintenance cost and makes it harder to keep behavior consistent.

Problem

• The same modal logic is implemented in both codebases.
• The modal should not be shown anymore.
• The JumpIn component in ui2 is the right place to centralize this logic.

Expected behavior

• Remove the modal behavior from jump-site.
• Reuse the JumpIn component from UI2, ensuring that all the logic for handling sign-in state and redirects lives in one place.

Proposed changes

1. Refactor jump-site to stop handling modal logic directly.
2. Import and reuse the JumpIn component from ui2.
3. Pass the required props (isSignedIn, downloadUrl, onboardingUrl) to the component.
4. Eliminate the duplicated modal-related code from jump-site.

Expected outcome

• A single source of truth for JumpIn logic in UI2.
• Cleaner code in jump-site without modal handling.
• Consistent user experience across dapps.