[IFEANYIBRIGHT]

closes #1494

Summary of Changes

1. TransactionBuilderService (src/services/transactionBuilder.ts)

• Added Soroban RPC simulation (simulateTransaction) and assembly (assembleTransaction) to produce XDR with sorobanData
• Changed BuildDepositParams from userPublicKey to userStellarAddress to use the user's Stellar address from their profile
• Added isBackendOwnedAccount option to only use sequence store for backend-owned accounts (prevents sequence burning for user-owned accounts)
• Added new response fields: resourceFee, minResourceFee, latestLedger
• Moved all error class definitions to top of file for proper TypeScript hoisting
• Used rpc.assembleTransaction instead of deprecated prepareTransaction API

2. DepositController (src/controllers/depositController.ts)

• Added userRepository dependency to fetch user's stellarAddress
• Returns 400 STELLAR_ADDRESS_REQUIRED when user lacks a Stellar address
• Updated response to include new metadata fields
• Fixed error handling for unknown error types

3. OpenAPI Specification (docs/openapi.json)

• Added /api/vault/deposit/prepare endpoint with full request/response schemas
• Added new metadata fields: resourceFee, minResourceFee, latestLedger
• Added STELLAR_ADDRESS_REQUIRED error example

4. Error Codes (docs/error-codes.yaml)

• Added STELLAR_ADDRESS_REQUIRED error code

5. Documentation (docs/deposit-transaction-builder.md)

• Updated response format with new fields
• Added simulation/assembly explanation
• Documented sequence store behavior for backend vs user-owned accounts

6. Tests

• Updated transactionBuilder.test.ts with new mocks for Soroban RPC and tests for simulation/assembly
• Updated depositController.test.ts with userRepository mock and new test cases
  Verification
• ✅ npm run typecheck - Passes for modified files (pre-existing errors in other files)
• ✅ npm run validate:openapi - Passes (46 paths, 60 operations)
• ✅ npm run build - Compiles successfully
• ⚠️ npm run lint - Fails due to Node.js version mismatch (pre-existing dependency issue)
• ⚠️ Tests - Quarantined in jest.quarantine.json, require JEST_RUN_QUARANTINED=1 to run

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