PR 3: Observability back-links and terminology cleanup

- Added an Observability back-link at the top of all 7 Observability-area pages (AuditLog, SystemLogs, SystemInfo, AiUsageReport, UsageQuota, BannedIps, Diagnostics/Index) consistent with the Maintenance back-link pattern from PR 2
- Renamed company-level nav label and view title from "Notification Log" to "Email & SMS Log" to distinguish it clearly from the platform-level "Platform Notifications", "Audit Log", and "System Logs" surfaces

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Views/NotificationLogs/Index.cshtml

@@ -1,6 +1,6 @@
 @model PowderCoating.Application.DTOs.Common.PagedResult<PowderCoating.Application.DTOs.Notification.NotificationLogDto>
 @{
-    ViewData["Title"] = "Notification Log";
+    ViewData["Title"] = "Email & SMS Log";
     ViewData["PageIcon"] = "bi-bell-history";
     var sortCol = ViewBag.SortColumn as string ?? "SentAt";
     var sortDir = ViewBag.SortDirection as string ?? "desc";