feat: add Quart app factory, config loader, and /api/health endpoint

Config reads from env vars (12-factor); .env.example documents defaults.
Health endpoint is liveness-only (no DB/Redis touch). Test added for CI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/__init__.py

@@ -0,0 +1,19 @@
+"""Quart app factory."""
+
+import logging
+
+from quart import Quart
+
+from .api import api_bp
+from .config import get_config
+
+
+def create_app() -> Quart:
+    cfg = get_config()
+    logging.basicConfig(level=cfg.log_level)
+
+    app = Quart(__name__)
+    app.secret_key = cfg.secret_key
+    app.register_blueprint(api_bp)
+
+    return app

backend/app/api/__init__.py

@@ -0,0 +1,8 @@
+"""API blueprint registration."""
+
+from quart import Blueprint
+
+from . import health
+
+api_bp = Blueprint("api", __name__, url_prefix="/api")
+api_bp.add_url_rule("/health", view_func=health.get_health, methods=["GET"])

backend/app/api/health.py

@@ -0,0 +1,5 @@
+"""Health endpoint — no DB or Redis touch; just liveness."""
+
+
+async def get_health():
+    return {"status": "ok"}, 200

backend/app/config.py

@@ -0,0 +1,52 @@
+"""Application configuration loaded from environment variables."""
+
+import os
+from dataclasses import dataclass
+from functools import lru_cache
+
+
+@dataclass(frozen=True)
+class Config:
+    db_user: str
+    db_password: str
+    db_host: str
+    db_port: int
+    db_name: str
+
+    celery_broker_url: str
+    celery_result_backend: str
+
+    secret_key: str
+    extension_api_key: str  # used by the Firefox extension; lands in FC-3 but read here
+    log_level: str
+
+    @property
+    def database_url(self) -> str:
+        return (
+            f"postgresql+asyncpg://{self.db_user}:{self.db_password}"
+            f"@{self.db_host}:{self.db_port}/{self.db_name}"
+        )
+
+    @property
+    def database_url_sync(self) -> str:
+        # Alembic uses sync driver
+        return (
+            f"postgresql+psycopg://{self.db_user}:{self.db_password}"
+            f"@{self.db_host}:{self.db_port}/{self.db_name}"
+        )
+
+
+@lru_cache(maxsize=1)
+def get_config() -> Config:
+    return Config(
+        db_user=os.environ.get("DB_USER", "fabledcurator"),
+        db_password=os.environ["DB_PASSWORD"],
+        db_host=os.environ.get("DB_HOST", "postgres"),
+        db_port=int(os.environ.get("DB_PORT", "5432")),
+        db_name=os.environ.get("DB_NAME", "fabledcurator"),
+        celery_broker_url=os.environ.get("CELERY_BROKER_URL", "redis://redis:6379/0"),
+        celery_result_backend=os.environ.get("CELERY_RESULT_BACKEND", "redis://redis:6379/0"),
+        secret_key=os.environ["SECRET_KEY"],
+        extension_api_key=os.environ.get("EXTENSION_API_KEY", ""),
+        log_level=os.environ.get("LOG_LEVEL", "INFO"),
+    )

backend/app/extensions.py

@@ -0,0 +1,14 @@
+"""Singleton extension instances; bound to the app in create_app()."""
+
+from sqlalchemy.ext.asyncio import AsyncEngine, async_sessionmaker, create_async_engine
+
+from .config import get_config
+
+
+def make_engine() -> AsyncEngine:
+    cfg = get_config()
+    return create_async_engine(cfg.database_url, pool_pre_ping=True, future=True)
+
+
+def make_session_factory(engine: AsyncEngine) -> async_sessionmaker:
+    return async_sessionmaker(engine, expire_on_commit=False)