Fix: Improve /admin/api-key endpoint with multiple file paths and DB fallback

Add: GET /admin/api-key endpoint to display seeded API key in UI

A4: Add projects, flows, flow_runs models and API endpoints

Fix: Make HTTPBearer return 401 instead of 403 when Authorization header is missing

A3: Add API key authentication and GET /me endpoint

A1: Add typed HealthResponse model with OpenAPI schema

Fix Core Phase 1: Add health endpoint, __init__.py files, and router registration

Restructure project: add models, alembic migrations, and core modules

Create health.py