feat(backend): initialisation du projet FastAPI

Structure en couches api / services / repositories / models, sens de
dependance unique, une session SQLAlchemy async injectee par dependance.

- Python 3.14, dependances gerees par uv et verrouillees dans uv.lock
- FastAPI expose par une factory : aucune configuration lue a l'import,
  ce qui rend tests et migrations independants de l'environnement
- Settings Pydantic, APP_SECRET_KEY et DATABASE_URL sans valeur par defaut
- Sondes /health/live et /health/ready, metriques Prometheus sur /metrics
- Lint et format ruff, mypy strict, pytest avec couverture
- Alembic branche sur DATABASE_URL et non sur alembic.ini
- Image Docker multi-stage, utilisateur non root, sonde de sante integree

apps/backend/app/core/config.py

@@ -0,0 +1,41 @@
+from functools import lru_cache
+from typing import Literal
+
+from pydantic import Field, SecretStr
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+Environment = Literal["local", "dev", "staging", "prod"]
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(
+        env_file=".env",
+        env_prefix="APP_",
+        env_file_encoding="utf-8",
+        extra="ignore",
+    )
+
+    name: str = "EnerVision API"
+    version: str = "0.1.0"
+    env: Environment = "local"
+    debug: bool = False
+    log_level: str = "INFO"
+    api_prefix: str = "/api/v1"
+    secret_key: SecretStr
+    cors_origins: str = ""
+    database_url: str = Field(validation_alias="DATABASE_URL")
+    database_pool_size: int = 5
+    database_max_overflow: int = 10
+
+    @property
+    def allowed_origins(self) -> list[str]:
+        return [origin.strip() for origin in self.cors_origins.split(",") if origin.strip()]
+
+    @property
+    def is_production(self) -> bool:
+        return self.env == "prod"
+
+
+@lru_cache
+def get_settings() -> Settings:
+    return Settings()

apps/backend/app/core/logging.py

@@ -0,0 +1,48 @@
+import logging
+from logging.config import dictConfig
+
+from app.core.config import Settings
+
+
+def configure_logging(settings: Settings) -> None:
+    formatter = "json" if settings.is_production else "console"
+    dictConfig(
+        {
+            "version": 1,
+            "disable_existing_loggers": False,
+            "formatters": {
+                "console": {
+                    "format": "%(asctime)s %(levelname)-8s %(name)s %(message)s",
+                },
+                "json": {
+                    "()": "pythonjsonlogger.json.JsonFormatter",
+                    "format": "%(asctime)s %(levelname)s %(name)s %(message)s",
+                },
+            },
+            "handlers": {
+                "default": {
+                    "class": "logging.StreamHandler",
+                    "formatter": formatter,
+                    "stream": "ext://sys.stdout",
+                },
+            },
+            "root": {"handlers": ["default"], "level": settings.log_level},
+            "loggers": {
+                "uvicorn": {
+                    "handlers": ["default"],
+                    "level": settings.log_level,
+                    "propagate": False,
+                },
+                "uvicorn.access": {
+                    "handlers": ["default"],
+                    "level": settings.log_level,
+                    "propagate": False,
+                },
+                "sqlalchemy.engine": {"level": "WARNING"},
+            },
+        }
+    )
+
+
+def get_logger(name: str) -> logging.Logger:
+    return logging.getLogger(name)