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/access_log.py

@@ -0,0 +1,32 @@
+"""Access log model for tracking user actions."""
+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import BigInteger, DateTime, ForeignKey, Index, Integer, JSON, String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from database import Base
+
+
+class AccessLog(Base):
+    __tablename__ = "access_logs"
+
+    id: Mapped[int] = mapped_column(BigInteger, primary_key=True, autoincrement=True)
+    user_id: Mapped[Optional[int]] = mapped_column(
+        Integer, ForeignKey("users.id"), nullable=True
+    )
+    action: Mapped[str] = mapped_column(String(100), nullable=False, index=True)
+    details: Mapped[Optional[dict]] = mapped_column(JSON, nullable=True)
+    ip_address: Mapped[Optional[str]] = mapped_column(String(45), nullable=True)
+    user_agent: Mapped[Optional[str]] = mapped_column(String(500), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime, nullable=False, server_default=func.now()
+    )
+
+    __table_args__ = (
+        Index("ix_access_log_user_time", "user_id", "created_at"),
+        {"mysql_engine": "InnoDB", "mysql_charset": "utf8mb4"},
+    )
+
+    def __repr__(self) -> str:
+        return f"<AccessLog user={self.user_id} action={self.action}>"