refactor(test): organize suite by clean-architecture layers

[develop-iro]

Summary

Reorganizes the test suite into a scalable test/ tree by clean-architecture layer, while the suite is still small enough to migrate cleanly.

test/
  domain/         # unit (*.spec.ts)
  application/    # use-case integration (*.integration.spec.ts)
  contracts/      # adapter contracts (*.contract.spec.ts)
  e2e/
    journeys/     # Playwright specs
    fixtures/     # ready data
    doubles/      # API route doubles
    support/      # page helpers
  support/        # shared fixtures/doubles for non-e2e layers

Changes

• Moved all src/**/*.spec.ts into the layer folders above (imports via @/)
• Extracted e2e mocks into test/e2e/{fixtures,doubles,support}
• Added @test/* path alias and sample test/support/fixtures/catalog-fund.ts
• Updated runners: test:unit → domain/application/contracts; Playwright testDir → ./test/e2e
• Documented in ADR-004, docs/architecture/testing-strategy.md, test/README.md, and .cursor/rules/testing-strategy.mdc

Test plan

• pnpm run test:unit (138 cases pass)
• pnpm run test:scripts
• pnpm run typecheck
• Pre-push test:ci including Playwright e2e
• Reviewer: confirm layer placement of borderline specs (e.g. analytics route resolution → contracts)