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/schemas/user.py

@@ -0,0 +1,65 @@
+"""Pydantic schemas for User operations."""
+from datetime import datetime
+from typing import Optional
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class UserCreate(BaseModel):
+    """Schema for creating a new user."""
+    username: str = Field(..., min_length=3, max_length=100)
+    password: str = Field(..., min_length=6, max_length=128)
+    email: Optional[str] = Field(None, max_length=255)
+    display_name: str = Field(..., min_length=1, max_length=255)
+    roles: list[str] = Field(default_factory=list)
+    is_admin: bool = False
+    language_pref: str = Field("it", pattern="^(it|en)$")
+    theme_pref: str = Field("light", pattern="^(light|dark)$")
+
+
+class UserUpdate(BaseModel):
+    """Schema for updating a user (admin)."""
+    email: Optional[str] = Field(None, max_length=255)
+    display_name: Optional[str] = Field(None, min_length=1, max_length=255)
+    roles: Optional[list[str]] = None
+    is_admin: Optional[bool] = None
+    active: Optional[bool] = None
+    language_pref: Optional[str] = Field(None, pattern="^(it|en)$")
+    theme_pref: Optional[str] = Field(None, pattern="^(light|dark)$")
+
+
+class UserProfileUpdate(BaseModel):
+    """Schema for user self-update (profile)."""
+    display_name: Optional[str] = Field(None, min_length=1, max_length=255)
+    language_pref: Optional[str] = Field(None, pattern="^(it|en)$")
+    theme_pref: Optional[str] = Field(None, pattern="^(light|dark)$")
+
+
+class UserResponse(BaseModel):
+    """Schema for user response."""
+    model_config = ConfigDict(from_attributes=True)
+
+    id: int
+    username: str
+    email: Optional[str] = None
+    display_name: str
+    roles: list[str]
+    is_admin: bool
+    language_pref: str
+    theme_pref: str
+    active: bool
+    created_at: datetime
+    last_login: Optional[datetime] = None
+
+
+class LoginRequest(BaseModel):
+    """Schema for login request."""
+    username: str
+    password: str
+
+
+class LoginResponse(BaseModel):
+    """Schema for login response."""
+    user: UserResponse
+    api_key: str
+    message: str = "Login successful"