feat: send sheet contacts navigates to coming soon

[ovitrif]

Closes #607

This PR adds a "Coming Soon" navigation option when tapping the Contacts button in the Send sheet, ensuring users see the placeholder screen instead of a dead-end.

Description

• Add Contacts button to the Send sheet that navigates to the Coming Soon screen
• Update AppViewModel to expose the Coming Soon navigation event
• Remove unused Contacts navigation from the Send Recipient screen

Preview

IMAGE_1

VIDEO_2

QA Notes

1. Send Sheet Contacts Navigation

   • Open the Send sheet from the wallet screen
   • Tap the "Contacts" button
   • Verify it navigates to the Coming Soon screen

2. Regression

   • Test regular send flow via QR scan still works
   • Test send flow via clipboard paste still works