Add `RecipientDashboard` claim button with Freighter signing

[ritik4ever]

Problem

RecipientDashboard.tsx shows claimable amount but the 'Claim' button may not submit a Soroban transaction signed by Freighter. It may only call the backend API.

Scope

Wire the Claim button to build, sign with Freighter, and submit the Soroban claim transaction directly.

Acceptance criteria

• Claim button disabled until Freighter wallet connected
• Shows estimated claimable amount before signing
• Submits claim(stream_id, recipient, amount) via Soroban after Freighter signs
• Transaction hash shown with Stellar Expert link on success
• Vitest test mocks Freighter and asserts transaction submitted

Complexity: High · 250 points

[espcris05-commits]

/attempt #391

I'd like to add RecipientDashboard claim button with Freighter signing.

Wallet USDC: GCR377MUJ75YKFLNZKT6XPWNDUIEDZDUHUWY5E2LHOBBSSJDU7MJRZXF
Wallet BNB: 0x6851F2cCD4C4EA991734FAA83c027A909f2703f3