refactor: enforce enum machine codes

Use owner enums for error and T-Bank protocol values with ESLint regression checks.

Preserve open wire fallbacks and keep protocol imports independent of DI and Prisma.

Verified npm ci, verify, 226 unit tests, 262 isolated e2e tests and unchanged OpenAPI.

src/integrations/tbank/tbank-access.service.ts

@@ -10,6 +10,7 @@ import type { TbankAccount } from './tbank.client';
 
 import { PrismaService } from '../../prisma/prisma.service';
 import { supportedTbankAccounts } from './tbank-account.policy';
+import { TbankErrorCode } from './tbank-error-code';
 import { tbankSourceNeedsRefresh } from './tbank-source.policy';
 import { TbankTokenService } from './tbank-token.service';
 
@@ -103,7 +104,7 @@ export class TbankAccessService {
         state: 'running',
         connection: { invalidToken: false },
       },
-      data: { state: 'failed', errorCode: 'TBANK_UNAVAILABLE' },
+      data: { state: 'failed', errorCode: TbankErrorCode.Unavailable },
     });
     return result.count === EXPECTED_UPDATED_CONNECTIONS;
   }
@@ -205,7 +206,7 @@ export class TbankAccessService {
     return this.prisma.$transaction(async (tx) => {
       const claimed = await tx.tbankSyncWork.updateMany({
         where: { ...attempt, state: 'running' },
-        data: { state: 'failed', errorCode: 'INVALID_TBANK_TOKEN' },
+        data: { state: 'failed', errorCode: TbankErrorCode.InvalidToken },
       });
       if (!claimed.count) return false;
       await tx.tbankConnection.update({
@@ -236,10 +237,10 @@ export class TbankAccessService {
       },
     });
     if (!connection) {
-      throw new ConflictException({ code: 'TBANK_NOT_CONNECTED' });
+      throw new ConflictException({ code: TbankErrorCode.NotConnected });
     }
     if (connection.invalidToken) {
-      throw new BadRequestException({ code: 'INVALID_TBANK_TOKEN' });
+      throw new BadRequestException({ code: TbankErrorCode.InvalidToken });
     }
     if (
       connection.membershipAt &&