feat(backend-sep12): GCS StorageProvider, UploadRecord schema, MIME validation & mock SMTP tests

[vic-Gray]

Summary

This PR implements four related backend issues in the backend-sep12 and backend-tests component scopes.

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Changes

#545 — [SEP-12] Implement GCS StorageProvider (closes #545)

• Added @google-cloud/storage: ^7.9.0 to backend/package.json
• Created StorageProvider interface (src/services/storage/storage.provider.ts)
  • Single method: getSignedUploadUrl(key, mimeType, expiresIn?): Promise<string>
• Created GcsStorageProvider implementing the interface (src/services/storage/gcs.storage.provider.ts)
  • Uses GCS v4 signed URLs with action: 'write', default TTL 900 s
  • Storage client injectable for easy unit-testing
• Barrel export via src/services/storage/index.ts

#547 — [SEP-12] Add UploadRecord Schema to Prisma (closes #547)

• Added UploadStatus enum (PENDING | COMPLETED | EXPIRED) to backend/prisma/schema.prisma
• Added UploadRecord model with fields:
  • id, account, fieldName, storageKey, status, expiresAt, createdAt, updatedAt
  • Indexes on account and status

#550 — [SEP-12] Add Content-Type Allowlist Validation (closes #550)

• Exported ALLOWED_MIME_TYPES set from src/api/routes/sep12.route.ts:
  image/jpeg, image/png, image/webp, application/pdf
• Added Multer fileFilter — rejects disallowed types via MulterError
• Added Express error-handler middleware returning HTTP 400 with a descriptive message listing allowed types

#541 — Add Mock SMTP Server for Local Backend Testing (closes #541)

• Added nodemailer-mock: ^2.0.5 to devDependencies
• Created src/services/admin-email.service.test.ts with 7 unit tests:
  • Sends exactly one email per call
  • Correct to and from addresses
  • Reset token present in plain-text body
  • Reset URL and token present in HTML body
  • Expiry timestamp present in body
  • Independent second send (models withdrawal confirmation pattern)

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Testing

# Prisma schema validation
npx prisma validate

# Backend unit tests (includes new SMTP mock tests)
npm run test:backend

Files Changed

File	Change
backend/package.json	Add @google-cloud/storage dep, nodemailer-mock devDep
backend/prisma/schema.prisma	Add UploadStatus enum + UploadRecord model
backend/src/api/routes/sep12.route.ts	MIME allowlist + fileFilter + 400 error handler
backend/src/services/storage/storage.provider.ts	NEW — StorageProvider interface
backend/src/services/storage/gcs.storage.provider.ts	NEW — GcsStorageProvider
backend/src/services/storage/index.ts	NEW — barrel export
backend/src/services/admin-email.service.test.ts	NEW — 7 SMTP mock tests

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