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/middleware/__init__.py

@@ -0,0 +1,22 @@
+"""FastAPI middleware for TieMeasureFlow."""
+from middleware.api_key import (
+    get_current_user,
+    require_role,
+    require_admin,
+    require_maker,
+    require_measurement_tec,
+    require_metrologist,
+    require_admin_user,
+)
+from middleware.logging import AccessLogMiddleware
+
+__all__ = [
+    "get_current_user",
+    "require_role",
+    "require_admin",
+    "require_maker",
+    "require_measurement_tec",
+    "require_metrologist",
+    "require_admin_user",
+    "AccessLogMiddleware",
+]