feat(storage): support deleting backends and improve admin UI

- Implement storage backend deletion, which automatically resets default storage settings and user-specific overrides when a backend is removed.
- Add unit tests covering the delete action and its cleanup side effects.
- Improve admin UI responsiveness, fixing table scrolling, flex wrapping, and text truncation for long storage backend names.
- Update security documentation to clarify trusted proxy configurations and explain how trusted proxies are protected from automatic bans.

backend/static/css/50-admin.css

@@ -1,11 +1,19 @@
 .admin-header,
 .table-header {
   display: flex;
+  min-width: 0;
   align-items: center;
   justify-content: space-between;
   gap: 1rem;
 }
 
+.admin-header > *,
+.table-header > *,
+.admin-grid-two > *,
+.logs-filter-card > * {
+  min-width: 0;
+}
+
 .kicker {
   margin: 0 0 0.4rem;
   color: var(--muted-foreground);
@@ -72,12 +80,15 @@
 }
 
 .admin-table-wrap {
+  max-width: 100%;
   overflow-x: auto;
   margin-top: 1rem;
+  -webkit-overflow-scrolling: touch;
 }
 
 .admin-table {
   width: 100%;
+  min-width: 46rem;
   border-collapse: collapse;
   font-size: 0.85rem;
 }
@@ -204,6 +215,7 @@
   display: flex;
   gap: 0.4rem;
   align-items: center;
+  flex-wrap: wrap;
   margin-top: 0.4rem;
 }