API key come hash SHA-256, una per sessione, TTL rinnovabile (#41)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/models/orm/__init__.py

@@ -1,5 +1,6 @@
 """SQLAlchemy models for TieMeasureFlow."""
 from src.backend.models.orm.user import User
+from src.backend.models.orm.api_key import ApiKey
 from src.backend.models.orm.recipe import Recipe, RecipeVersion
 from src.backend.models.orm.task import RecipeTask, RecipeSubtask
 from src.backend.models.orm.measurement import Measurement
@@ -11,6 +12,7 @@ from src.backend.models.orm.vision import VisionReferenceImage, VisionResult
 
 __all__ = [
     "User",
+    "ApiKey",
     "Recipe",
     "RecipeVersion",
     "RecipeTask",