feat: FASE 1 - Backend Core (modelli, auth, API)

Implementazione completa del backend FastAPI:
- Modelli SQLAlchemy: User, Recipe, RecipeVersion, RecipeTask,
  RecipeSubtask, Measurement, AccessLog, SystemSetting, RecipeVersionAudit
- Schemas Pydantic v2 per tutti i CRUD + statistiche SPC
- Middleware: API Key auth (X-API-Key) con role checking + access logging
- Router: auth, users, recipes, tasks, measurements, files, settings
- Services: auth (bcrypt+secrets), recipe (copy-on-write versioning),
  measurement (auto pass/fail con UTL/UWL/LWL/LTL)
- Alembic env.py con import modelli attivi
- Fix architect review: no double-commit, recipe_id subquery filter,
  user_id in access logs, type annotations corrette

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/models/user.py

@@ -0,0 +1,48 @@
+"""User model with combinable roles and admin flag."""
+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import Boolean, DateTime, Enum, Integer, JSON, String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from database import Base
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    username: Mapped[str] = mapped_column(String(100), unique=True, nullable=False, index=True)
+    password_hash: Mapped[str] = mapped_column(String(255), nullable=False)
+    email: Mapped[Optional[str]] = mapped_column(String(255), nullable=True)
+    display_name: Mapped[str] = mapped_column(String(255), nullable=False)
+
+    # Roles: combinable JSON array of "Maker", "MeasurementTec", "Metrologist"
+    roles: Mapped[list] = mapped_column(JSON, nullable=False, default=list)
+    # Admin flag separate from roles
+    is_admin: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+
+    # User preferences
+    language_pref: Mapped[str] = mapped_column(
+        Enum("it", "en", name="language_enum"), nullable=False, default="it"
+    )
+    theme_pref: Mapped[str] = mapped_column(
+        Enum("light", "dark", name="theme_enum"), nullable=False, default="light"
+    )
+
+    # Status
+    active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    api_key: Mapped[Optional[str]] = mapped_column(String(64), unique=True, nullable=True, index=True)
+
+    # Timestamps
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime, nullable=False, server_default=func.now()
+    )
+    last_login: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
+
+    def has_role(self, role: str) -> bool:
+        """Check if user has a specific role."""
+        return role in (self.roles or [])
+
+    def __repr__(self) -> str:
+        return f"<User {self.username} roles={self.roles}>"