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/config.py

@@ -0,0 +1,33 @@
+"""Application configuration.
+
+Twelve-factor: everything is read from the environment. Defaults are
+development-friendly; production supplies real values via the compose `.env`.
+No secrets or endpoints are hard-coded.
+"""
+
+from functools import lru_cache
+
+from pydantic import Field
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(
+        env_file=".env",
+        env_file_encoding="utf-8",
+        extra="ignore",
+    )
+
+    app_name: str = "Provenance"
+    version: str = "0.0.0"
+    app_env: str = Field(default="development", description="development | production")
+
+    # SQLAlchemy async URL, e.g. postgresql+asyncpg://user:pass@host:5432/db
+    database_url: str = Field(
+        default="postgresql+asyncpg://provenance:provenance@localhost:5432/provenance",
+    )
+
+
+@lru_cache
+def get_settings() -> Settings:
+    return Settings()

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