docs: add email verification endpoints to OpenAPI spec (#449)

[s6pa1rta3n-lab]

Description

Addresses #449 by documenting the email notification and verification endpoints in docs/openapi.yaml.

Changes Included

• Added Notifications tag for notification and identity lifecycle endpoints.
• Documented POST /notifications/email:
  • Requires Bearer authentication (bearerAuth).
  • Request body accepting email with format email.
  • Responses for dispatched verification (200), generic anti-enumeration response (200), invalid email validation (400), unauthorized (401), and internal error (500).
• Documented GET /notifications/email/verify:
  • Public endpoint consuming query parameter token.
  • Responses for successful verification (200), idempotent repeated verification (200), invalid/expired token (400), and internal error (500).
• Added schema definitions for email identity status and responses:
  • EmailIdentityStatus enum: PENDING, VERIFIED, BOUNCED, COMPLAINED, SUPPRESSED.
  • RequestEmailVerificationRequest schema.
  • GenericEmailVerificationResponse schema.
  • PendingEmailIdentity and VerifiedEmailIdentity schemas.
  • PendingEmailVerificationResponse and VerifiedEmailVerificationResponse schemas.
  • EmailVerificationResponse oneOf union schema.
  • EmailIdentity schema.
• Resolved Redocly no-identical-paths error by consolidating /alerts/{userId} and /alerts/{id} paths under /alerts/{id}.
• Added comprehensive unit tests in tests/unit/docs/openapi-notifications.test.ts verifying OpenAPI contract and specification compliance.

Verification

• npm run validate:spec passes cleanly.
• npx @redocly/cli bundle docs/openapi.yaml --output /tmp/openapi-bundled.yaml resolves all refs without error.
• npx jest tests/unit/docs/openapi-notifications.test.ts passes (4/4 tests).
• npx jest tests/unit/controllers/email-identity-controller.test.ts passes (29/29 tests).

Closes #449

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