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/js/20-storage-admin.js

@@ -1,4 +1,16 @@
 (function () {
+  document.querySelectorAll("[data-storage-delete-warning]").forEach((button) => {
+    button.addEventListener("click", (event) => {
+      const name = button.getAttribute("data-storage-delete-warning") || "this storage backend";
+      const confirmed = window.confirm(
+        `Delete ${name}?\n\nAll boxes stored on this location will also be deleted. Any global defaults or user storage overrides pointing at it will be reset back to inherited local storage.`
+      );
+      if (!confirmed) {
+        event.preventDefault();
+      }
+    });
+  });
+
   document.querySelectorAll("[data-storage-speed-open]").forEach((button) => {
     button.addEventListener("click", () => {
       const modal = document.querySelector("[data-storage-speed-modal]");