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/services/auth_service.py

@@ -0,0 +1,97 @@
+"""Authentication service - password hashing, API key management."""
+import secrets
+from datetime import datetime
+
+from passlib.context import CryptContext
+from sqlalchemy import select, update
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from models.user import User
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+
+def hash_password(password: str) -> str:
+    """Hash a password using bcrypt."""
+    return pwd_context.hash(password)
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    """Verify a password against its hash."""
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def generate_api_key() -> str:
+    """Generate a secure 64-character API key."""
+    return secrets.token_urlsafe(48)  # 64 chars base64
+
+
+async def authenticate_user(
+    db: AsyncSession, username: str, password: str
+) -> User | None:
+    """Authenticate user by username and password."""
+    result = await db.execute(
+        select(User).where(User.username == username, User.active == True)
+    )
+    user = result.scalar_one_or_none()
+    if user is None or not verify_password(password, user.password_hash):
+        return None
+    return user
+
+
+async def login_user(db: AsyncSession, user: User) -> str:
+    """Generate API key and update last_login for user."""
+    api_key = generate_api_key()
+    await db.execute(
+        update(User)
+        .where(User.id == user.id)
+        .values(api_key=api_key, last_login=datetime.utcnow())
+    )
+    await db.flush()
+    return api_key
+
+
+async def logout_user(db: AsyncSession, user: User) -> None:
+    """Invalidate user's API key."""
+    await db.execute(
+        update(User).where(User.id == user.id).values(api_key=None)
+    )
+    await db.flush()
+
+
+async def create_user(
+    db: AsyncSession,
+    username: str,
+    password: str,
+    display_name: str,
+    email: str | None = None,
+    roles: list[str] | None = None,
+    is_admin: bool = False,
+    language_pref: str = "it",
+    theme_pref: str = "light",
+) -> User:
+    """Create a new user with hashed password."""
+    user = User(
+        username=username,
+        password_hash=hash_password(password),
+        display_name=display_name,
+        email=email,
+        roles=roles or [],
+        is_admin=is_admin,
+        language_pref=language_pref,
+        theme_pref=theme_pref,
+    )
+    db.add(user)
+    await db.flush()
+    await db.refresh(user)
+    return user
+
+
+async def regenerate_api_key(db: AsyncSession, user_id: int) -> str:
+    """Regenerate API key for a user."""
+    new_key = generate_api_key()
+    await db.execute(
+        update(User).where(User.id == user_id).values(api_key=new_key)
+    )
+    await db.flush()
+    return new_key