Batch send UI for splitter contract

[truthixify]

Tier: L (1-2 weeks) Type: feature

Context

stealth-splitter (PR #42) shipped but has no demo UX. Build a "split a payment among N recipients" flow.

Scope

• New page /split (or modal on Send page)
• Form: list of (recipient meta-address, weight), single funded amount
• Compute weighted shares; surface dust handling
• Build split definition, fund split atomically
• Show success state with per-recipient stealth addresses

Acceptance criteria

• Page or modal implemented
• Per-recipient validation
• Successful flow demo'd end-to-end on testnet
• Playwright test

Files to start with

• src/components/StellarSend.tsx (extend)
• New: src/components/StellarSplit.tsx