fix: wire real XDR generation into liquidity deposit/withdraw

[Godfrey-Delight]

🔗 Related Issue

Closes #1

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🔖 Title

Wire real XDR generation into liquidity deposit/withdraw

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📝 Description

Wires the real LiquidityContractClient into LiquidityService for deposit and withdraw, replacing the hardcoded placeholder XDR strings that were blocking the sponsor deposit flow end-to-end. LIQUIDITY_POOL_CONTRACT_ID is read via ConfigService, and contract simulation errors (codes 100–104) are mapped to typed BadRequestExceptions instead of surfacing raw Soroban errors.

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🔄 Changes Made

• Restored liquidity-contract.client.ts with buildUnsignedXdr (build, simulate, assemble unsigned envelope), and added blockchain.module.ts to provide it via SorobanService
• Wired LiquidityService deposit/withdraw to the real client, mapping contract simulation errors to typed HTTP 400s instead of placeholder XDR
• Updated unit and e2e tests (20 passing) to mock the client, assert correct invocation, and verify returned XDR parses via TransactionBuilder.fromXDR()

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📸 Screenshots (if applicable)

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🗒️ Additional Notes

-npm run build passes with zero TypeScript errors, no new any types introduced

-E2E tests run against mocked RPC simulation responses rather than a live Soroban testnet RPC — worth flagging since the acceptance criteria specifically asks for the e2e test to pass against a running testnet RPC; happy to add that run if a testnet endpoint/funded account is available in CI, or confirm this mock-based coverage is sufficient

-No schema changes, so no new migration file

[EmeditWeb]

Review verdict: ✅ APPROVE with minor corrections

Solid money-path work. The new liquidity client and service wiring are clean:

• STROOPS = 10_000_000n and Math.round(amount * 10_000_000) — correct 7-decimal conversion (avoids the * 100 bug fixed in #89).
• Share-price math for deposit/withdraw; proper service/client separation; BadRequestException on failure; no any in the new client; e2e + unit tests added. CI green.

Minor corrections:

1. liquidity.service.ts:279 — handleContractError(error: any, operation: string) uses any. Per code-standards, use unknown and narrow (e.g. error instanceof Error).
2. Cross-verify the deposit/withdraw 2-arg call signatures against the deployed liquidity-pool contract (same class of check as #90 for repay; lower risk since deposit/withdraw are simpler and more stable).

Merge-ready once the any is addressed.