refactor: replace internal UnitOfWork with NotificationUnitOfWork and NotificationBaseRepository

- Consolidate unit of work implementation with NotificationUnitOfWork.
- Refactor repositories to use NotificationBaseRepository for consistency.
- Simplify request handlers by removing IUnitOfWork dependency.
- Update related tests and service registration.

HrynCo.NotificationService.Web/wwwroot/css/admin.css

@@ -118,9 +118,10 @@ body {
 .empty-state .bi { font-size: 2.5rem; opacity: .35; display: block; margin-bottom: .75rem; }
 .empty-state p { font-size: .9rem; margin-bottom: 0; }
 
-/* ── Editor wrapper — constrains width ───────────────── */
+/* ── Editor wrapper ──────────────────────────────────── */
 .editor-wrapper {
-    max-width: 860px;
+    width: 100%;
+    max-width: none;
 }
 
 /* ── Editor card ──────────────────────────────────────── */
@@ -154,6 +155,26 @@ body {
     border-radius: 0 0 .5rem .5rem !important;
 }
 
+/* ── Editor tabs ─────────────────────────────────────── */
+.template-editor-tabs {
+    border-bottom-color: #dce3eb;
+}
+
+.template-editor-tabs .nav-link {
+    color: #526072;
+    font-weight: 600;
+    border-radius: .5rem .5rem 0 0;
+}
+
+.template-editor-tabs .nav-link.active {
+    color: #0d6efd;
+}
+
+/* ── Tab content ──────────────────────────────────────── */
+.tab-content {
+    min-width: 0;
+}
+
 /* ── Email template preview ───────────────────────────── */
 .template-preview-panel {
     border: 1px solid #dce3eb;
@@ -185,9 +206,9 @@ body {
     margin-top: .15rem;
 }
 
-.template-preview-grid {
+.template-preview-body {
     display: grid;
-    grid-template-columns: minmax(240px, 300px) minmax(0, 1fr);
+    grid-template-columns: minmax(0, 1fr);
     gap: 1rem;
     padding: 1rem 1.25rem 1.25rem;
 }
@@ -197,6 +218,13 @@ body {
     min-width: 0;
 }
 
+.template-preview-section-block {
+    padding: 1rem;
+    border: 1px solid #e5ebf2;
+    border-radius: .65rem;
+    background: #fafcff;
+}
+
 .template-preview-section-title {
     font-size: .7rem;
     font-weight: 700;
@@ -210,6 +238,7 @@ body {
     display: flex;
     flex-direction: column;
     gap: .75rem;
+    max-width: 420px;
 }
 
 .template-preview-variables .form-control-sm {
@@ -248,7 +277,7 @@ body {
 }
 
 @media (max-width: 992px) {
-    .template-preview-grid {
+    .template-preview-body {
         grid-template-columns: 1fr;
     }