Add comprehensive end-to-end pipeline test

[PAMulligan]

Description

Create an end-to-end test that runs the full `/build-from-schema` pipeline against a sample OpenAPI spec and verifies the output at every phase.

Why

The pipeline is Nerva's core value proposition. Without an E2E test, there's no automated verification that the 10-phase pipeline produces a working API. This is the most critical test the project can have — it validates that all skills, agents, and scripts work together correctly.

Acceptance Criteria

• Create a sample OpenAPI spec (`tests/fixtures/petstore.yaml`) with:
  • 2-3 resources (pets, owners)
  • CRUD operations
  • Auth requirements
  • Relations between resources
• Create a test harness that runs the pipeline phases in sequence
• Verify after each phase:
  • Phase 0: `build-spec.json` exists and is valid JSON
  • Phase 1: Drizzle schema files exist with correct tables
  • Phase 2: Integration test files exist and fail (RED)
  • Phase 3: Route handler files exist
  • Phase 5: Tests pass (GREEN)
  • Phase 8: Deployment config files exist
  • Phase 9: Build report exists
• Run as a separate CI workflow (not on every push — resource intensive)
• CI workflow has a manual trigger for on-demand testing
• Document how to run the E2E test locally

Notes

This test requires a running PostgreSQL instance. Use Docker Compose or `testcontainers` in CI.