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/templates/pages/admin_storage.html

@@ -76,6 +76,7 @@
                 {{if eq .Config.ID "local"}}<span class="badge">Required</span>
                 {{else if .Config.Enabled}}<span class="badge badge-active">Enabled</span>
                 {{else}}<span class="badge badge-disabled">Disabled</span>{{end}}
+                {{if .InUseReason}}<span class="badge" title="{{.InUseReason}}">In use</span>{{end}}
                 {{if .UsageLabel}}<span class="storage-card-usage">{{.UsageLabel}}</span>{{end}}
               </div>
             </div>
@@ -92,15 +93,9 @@
             {{end}}
             {{if ne .Config.ID "local"}}
             <a class="button button-outline button-sm" href="/admin/storage/{{.Config.ID}}/edit">Edit</a>
-            {{if .Config.Enabled}}
-            <form action="/admin/storage/{{.Config.ID}}/disable" method="post">
-              <input type="hidden" name="csrf_token" value="{{$.CSRFToken}}">
-              <button class="button button-outline button-sm" type="submit" {{if .InUse}}disabled title="Backend is in use"{{end}}>Disable</button>
-            </form>
-            {{end}}
             <form action="/admin/storage/{{.Config.ID}}/delete" method="post">
               <input type="hidden" name="csrf_token" value="{{$.CSRFToken}}">
-              <button class="button button-danger button-sm" type="submit" {{if .InUse}}disabled title="Backend is in use"{{end}}>Delete</button>
+              <button class="button button-danger button-sm" type="submit" data-storage-delete-warning="{{.Config.Name}}">Delete</button>
             </form>
             {{end}}
           </div>