feat: MultiSig

[tfrg]

What type of PR is this?

• feature

What this PR does:

Description

Multiple signers can sequentially add signatures, and each signature accumulates to ultimately generate a complete multi-signature document.

Changes

• SignDocument API
  • Added new SignDocument injection method to support multi-signature
  • Implemented signature accumulation logic that appends new signatures to existing signatures array
• UI
  • Signer Field: Displays current signature count and provides access to full signer list
    • Conditionally hidden for first signer to streamline initial signing experience
  • Signer List Page: Comprehensive view showing:
    • Signer information with wallet addresses
    • Signature status (signed/pending)
    • Action buttons (copy address, view on Gnoscan)