Add path payment route explorer

[MJ-RWA]

Complexity: High — 200 pts

Summary

Stellar's DEX supports multi-hop path payments through intermediate assets. StellarFlow's swap picks the first Horizon result automatically. This issue builds a dedicated Path Explorer that shows all available routes between two assets, ranked by output, so users can pick the best one.

Files to Create/Modify

• Create: src/pages/PathExplorerPage.tsx
• Modify: src/lib/stellar.ts — add findAllPaths and PathOption
• Modify: src/pages/SwapPage.tsx — add "Explore routes" link, read path URL param
• Modify: src/App.tsx — add /paths route
• Modify: src/types/index.ts — add PathOption type

Implementation Notes

findAllPaths in stellar.ts

export interface PathOption {
  rank: number;
  pathLabels: string[];
  pathAssets: StellarSdk.Asset[];
  destinationAmount: string;
  rate: string;
  isBest: boolean;
}
export async function findAllPaths(fromAssetCode, toAssetCode, amount, fromIssuer?, toIssuer?): Promise<PathOption[]>

Call server.strictSendPaths(sendAsset, amount, [destAsset]).call(), map each record to a PathOption with the full asset chain as pathLabels, sort descending by destinationAmount, mark index 0 as isBest.

PathExplorerPage layout

From: [XLM ▾]  To: [USDC ▾]  Amount: [100]  [Find Routes]
★ Best   XLM → USDC      You get: 41.23 USDC   [Use this route]
#2       XLM → yXLM → USDC   You get: 41.18 USDC   [Use this route]

"Use this route" navigates to /swap?from=XLM&to=USDC&amount=100&path=.... Empty state: "No routes found. Try a smaller amount."

SwapPage update

Read a path URL param and pre-select it, skipping the quote fetch and using the provided pathAssets directly. Add an "Explore routes" link below the quote details card.

Acceptance Criteria

• All Horizon-returned paths displayed and sorted by destination amount (highest first)
• Best route clearly labeled with ★ or "Best Rate" badge
• Each route shows the full intermediate asset chain as a visual breadcrumb
• "Use this route" navigates to Swap with the selected path pre-loaded
• Swap page accepts and uses a pre-selected path from URL params
• Empty state shown when Horizon returns no paths
• Works for any asset pair supported by the user's balance
• Works on Stellar mainnet

Screen Recording Requirements

1. From the Swap page, click "Explore routes"
2. Path Explorer opens pre-filled with current swap params
3. Multiple route options appear sorted by output amount
4. Best route has ★ badge
5. Click "Use this route" on the second-best route → navigated to Swap pre-filled with that exact route
6. Execute the swap → confirm the route used on Stellar Expert matches what was selected