Add multi-asset support with trustline management

[MJ-RWA]

Complexity: High — 200 pts

Summary

StellarFlow currently only supports XLM and USDC. This issue adds a "Manage Assets" page where users can discover and add trustlines for additional Stellar-issued assets (wBTC, yXLM, etc.), and dynamically updates the Send and Swap pages to support any asset the user holds.

Files to Create/Modify

• Create: src/lib/assets.ts — KNOWN_ASSETS registry (code, issuer, name, logo)
• Create: src/pages/ManageAssetsPage.tsx
• Modify: src/lib/stellar.ts — add buildChangeTrustTx
• Modify: src/pages/SendPage.tsx — dynamic asset list from balances
• Modify: src/pages/SwapPage.tsx — dynamic asset selectors
• Modify: src/App.tsx — add /assets route
• Modify: src/pages/DashboardPage.tsx — add "Manage Assets" link

Implementation Notes

assets.ts

Define a KNOWN_ASSETS: StellarAsset[] array with at least 4 assets beyond USDC (e.g. yXLM, AQUA) — each with code, issuer, name, logoSymbol.

buildChangeTrustTx in stellar.ts

export async function buildChangeTrustTx(sourceAddress, assetCode, assetIssuer, remove = false): Promise<string>

Uses Operation.changeTrust({ asset, limit: remove ? '0' : undefined }).

ManageAssetsPage

• List KNOWN_ASSETS with an "Added" badge for assets already in balances
• "Add" → build, sign, submit changeTrust tx
• "Remove" → only enabled when balance is 0
• Search bar filters by code or name

Dynamic selectors

Update SendPage and SwapPage to derive their asset dropdown options from the live balances array instead of a hardcoded XLM/USDC list.

Acceptance Criteria

• Manage Assets page lists at least 4 known assets beyond XLM and USDC
• Add button creates a changeTrust operation signed by Freighter
• Remove button only enabled when asset balance is 0
• New assets appear in Send and Swap selectors after trustline is added
• Search bar filters the asset list
• Works on Stellar mainnet

Screen Recording Requirements

1. Open Manage Assets → list of known assets
2. Click Add on yXLM → Freighter sign → trustline added
3. Dashboard now shows yXLM with 0 balance
4. Send page asset selector now includes yXLM
5. Remove yXLM trustline (balance 0) → disappears from Dashboard