Add KeyTeleport send flow

[praveenperera]

Parent issue: #618

Summary

Add the user-facing send flow for Key Teleport so Cove can originate supported secrets to another Key Teleport receiver.

Scope

• add a Key Teleport send entry point for wallets that actually have secret material available locally
• ingest the recipient packet by QR, pasted/shared link, or equivalent transport surface
• accept the recipient numeric verification code
• let the user choose a supported payload to send:
  • mnemonic
  • xprv
• generate the outgoing payload and teleport password
• present the result as QR / BBQr and shareable link
• make it clear that the teleport password must be delivered separately
• ensure wallets without local secret material are not eligible senders

Out of scope

• multisig PSBT teleport
• secure notes / backups / vault exports
• acting as a sender for watch-only or hardware-export-only wallets

Notes

This issue is about Cove participating as the sender, not just relaying an already-built payload.