feat: timer intervallo misura su ricetta + auto-logout per inattività

- Recipe: nuovo campo measurement_interval_minutes (migration 003) con UI nel recipe editor
- Auto-logout: impostazione di sistema configurabile da admin/settings, timer inattività JS
  con warning modale 60s prima del logout, tracking eventi utente throttled
- Navbar: aggiunto link "Impostazioni" per admin (desktop + mobile)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/backend/models/api/recipe.py

@@ -14,6 +14,7 @@ class RecipeCreate(BaseModel):
     name: str = Field(..., min_length=1, max_length=255)
     description: Optional[str] = None
     image_path: Optional[str] = Field(None, max_length=500)
+    measurement_interval_minutes: Optional[int] = Field(None, ge=1, le=1440)
     # Optional task-level fields for the initial technical drawing
     file_path: Optional[str] = Field(None, max_length=500)
     file_type: Optional[str] = Field(None, pattern="^(image|pdf)$")
@@ -25,6 +26,7 @@ class RecipeUpdate(BaseModel):
     name: Optional[str] = Field(None, min_length=1, max_length=255)
     description: Optional[str] = None
     image_path: Optional[str] = Field(None, max_length=500)
+    measurement_interval_minutes: Optional[int] = Field(None, ge=1, le=1440)
     change_notes: Optional[str] = None
     # Task-level fields: saved to the first task of the new version
     file_path: Optional[str] = Field(None, max_length=500)
@@ -55,6 +57,7 @@ class RecipeResponse(BaseModel):
     name: str
     description: Optional[str] = None
     image_path: Optional[str] = None
+    measurement_interval_minutes: Optional[int] = None
     created_by: int
     created_at: datetime
     active: bool