test: migrate web forgot password controller tests to testcontainers

[YB0y]

Summary

Migrate tests from api/tests/unit_tests/controllers/web/test_web_forgot_password.py to testcontainers integration tests at api/tests/test_containers_integration_tests/controllers/web/test_web_forgot_password.py.

Replaced Flask(__name__) with flask_app_with_containers fixture. All 5 tests migrated: email normalization before sending reset email, email normalization for validity checks, token email case preservation, account fetching with case fallback, and password update with commit verification. External services (AccountService, Session, db) remain mocked as tests verify controller routing and email normalization logic.

Part of #32454

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues.
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint and make type-check (backend) and cd web && npx lint-staged (frontend) to appease the lint gods

[github-actions]

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