refactor(handlers): standardize logging using request attributes helper

- Replace manual IP logging with the `withRequestLogAttrs` helper in authentication handlers.
- Add user activity logging for API documentation and login page views.
- Clean up log calls to use variadic expansion of request attributes.

backend/libs/handlers/pages.go

@@ -46,6 +46,17 @@ func (a *App) Home(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "unable to load upload policy", http.StatusInternalServerError)
 		return
 	}
+	actor := "anonymous"
+	if loggedIn {
+		actor = "user"
+	}
+	a.logger.Info("upload page viewed", withRequestLogAttrs(r,
+		"source", "page",
+		"severity", "user_activity",
+		"code", 2500,
+		"actor", actor,
+		"user_id", user.ID,
+	)...)
 	maxUploadSize, limitSummary := a.homeUploadPolicyLabels(settings, user, loggedIn, isAdmin)
 	expiryOptions, defaultExpiry := a.homeExpiryOptions(settings, user, loggedIn, isAdmin)
 	a.renderPage(w, r, http.StatusOK, "home.html", web.PageData{