Stabilize the full test suite in CI

[fdaei]

Context

The initial GitHub Actions run generated the Prisma client successfully and passed typechecking and linting, but the full test command reported:

• 39 passing test suites
• 5 failing test suites
• 288 passing tests
• 7 failing tests

Affected areas include:

• payment gateway redirect behavior
• authorization boundary expectations
• architecture boundary expectations
• admin dashboard configuration
• Redis service configuration

Some failures are caused by required test environment variables not being defined; others are assertion or architecture-policy mismatches.

Acceptance criteria

• Document all environment variables required by unit tests
• Provide safe test defaults or a dedicated test environment loader
• Fix the authorization and architecture expectation mismatches
• Make npm test pass from a clean checkout
• Restore npm test as a required CI step
• Keep database-dependent integration tests isolated from unit tests

Reproduction

npm ci
DATABASE_URL=postgresql://postgres:postgres@localhost:5432/lingospeak npm run db:generate
npm test