fix(sdk-core): stamp enterprise-id header on getVaultConfig call

DefiVault.getVaultConfig() was calling the defi-service vault config
endpoint without the `enterprise-id` header that defi-service requires.
This caused the entire deposit flow to fail for UI clients whose access
tokens don't have `accessToken.enterprise` populated as a fallback in
WP's auth resolution.

Fix: call `.set('enterprise-id', this.wallet.toJSON().enterprise)` on
the GET request. The enterprise id is sourced directly from the wallet
context via the IWallet.toJSON() accessor — no constructor change needed.

Tests: add `enterprise: 'test-enterprise-id'` to mock wallet data,
add `set: sinon.stub().returnsThis()` to mockRequest helper, and assert
`.set('enterprise-id', 'test-enterprise-id')` is called on the GET.

Ticket: DEFI-496
Session-Id: 1434552b-96ce-4eac-9922-cc2288aa5054
Task-Id: ba541f90-9eb1-45ed-a30f-a0605abde178

Author: venkateshv1266

modules/sdk-core/src/bitgo/defi/defiVault.ts

@@ -65,6 +65,7 @@ export class DefiVault implements IDefiVault {
     }
     const raw = await this.bitgo
       .get(this.bitgo.microservicesUrl(`/api/defi-service/v1/vaults/${params.vaultId}`))
+      .set('enterprise-id', this.wallet.toJSON().enterprise)
       .result();
     return decodeWithCodec(GetVaultResponse, raw, 'getVaultConfig');
   }

modules/sdk-core/test/unit/bitgo/defi/defiVault.ts

@@ -14,6 +14,7 @@ describe('DefiVault', function () {
   function mockRequest(result: any) {
     return {
       send: sinon.stub().returnsThis(),
+      set: sinon.stub().returnsThis(),
       query: sinon.stub().returnsThis(),
       result: sinon.stub().resolves(result),
     };
@@ -71,6 +72,7 @@ describe('DefiVault', function () {
       id: 'test-wallet-id',
       coin: 'eth',
       keys: ['user-key', 'backup-key', 'bitgo-key'],
+      enterprise: 'test-enterprise-id',
     };
 
     wallet = new Wallet(mockBitGo, mockBaseCoin, mockWalletData);
@@ -110,6 +112,7 @@ describe('DefiVault', function () {
 
       result.should.deepEqual(vaultConfig);
       mockBitGo.get.calledWith('https://bitgo.com/api/defi-service/v1/vaults/vlt-concrete-1').should.be.true();
+      req.set.calledWith('enterprise-id', 'test-enterprise-id').should.be.true();
     });
 
     it('should throw if vaultId is missing', async function () {