Scaffold FastAPI backend skeleton with health probes

Phase 0 foundation. uv-managed FastAPI app (package=false, runs from source via uv run). Layered seams in place: app/api for routers, app/core for config (pydantic-settings, fully env-driven) and the async SQLAlchemy engine; service/repository/domain layers land with the data model.

Exposes /health (liveness) and /health/ready (Postgres reachability via SELECT 1, 503 on failure) so the deploy wiring is verifiable before any data model exists. Includes a liveness test and the resolved uv.lock. Ignore pytest/ruff/mypy caches.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/core/db.py

@@ -0,0 +1,22 @@
+"""Async database engine.
+
+A single lazily-created async engine for the process. The repository layer
+(coming with the data model) will build sessions on top of this; for now it
+backs the readiness probe.
+"""
+
+from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine
+
+from app.core.config import get_settings
+
+_engine: AsyncEngine | None = None
+
+
+def get_engine() -> AsyncEngine:
+    global _engine
+    if _engine is None:
+        _engine = create_async_engine(
+            get_settings().database_url,
+            pool_pre_ping=True,
+        )
+    return _engine