feat(user-perf): add ui user-perf + dotfile filter

- add resource kind filter (file, folder, drive) in shared section (localStorage stored)
- add user preferences serverside store
- add client side dotfile filter (show/hide dotfiles) (user perf stored, default: dotfiles are shown)
  for security trashed dotfile are always displayed

  protection added: if a folder has only hidden items, a notification invite user to display it
  if a user rename or create a hidden item, a notification tells it to user

frontend/src/lib/utils/dotfileFilter.ts

@@ -0,0 +1,53 @@
+/**
+ * Unix-style dotfile hide convention.
+ *
+ * A file / folder is considered "hidden" when its display name starts
+ * with a `.`. This matches the convention used by every Unix shell,
+ * macOS Finder (with Cmd+Shift+.), and every cloud-share product that
+ * offers a hide toggle (Nextcloud, ownCloud, Seafile).
+ *
+ * Windows-style HIDDEN attribute is not honoured — the attribute isn't
+ * preserved across upload / dedup, and OxiCloud stores content-
+ * addressable blobs without any filesystem metadata carrier. Matches
+ * Nextcloud desktop client behaviour, which also strips HIDDEN on
+ * upload.
+ *
+ * Scope: this helper is UI cosmetics ONLY. A direct URL to a hidden
+ * file (`/files/<uuid>`) still resolves; batch operations only touch
+ * what the UI actually rendered; WebDAV / NC / CalDAV surfaces are
+ * unaffected because they consume the raw API responses. The whole
+ * filter lives at the render layer, keyed on
+ * `preferences.hideDotfiles`.
+ */
+
+/** True when the name is a Unix-style hidden file (leading `.`). */
+export function isDotfile(name: string): boolean {
+	return name.startsWith('.');
+}
+
+/**
+ * Filter an array of `{ name }`-shaped items down to the visible set.
+ * When `hide` is `false`, returns the input array reference unchanged
+ * (no allocation, no derived recomputation churn); when `hide` is
+ * `true`, returns a new array with dotfiles removed.
+ *
+ * `T extends { name: string }` matches `FileItem`, `FolderItem`,
+ * `SearchHit`, and the mixed `ResourceList` union without further
+ * type gymnastics at the call sites.
+ */
+export function filterDotfiles<T extends { name: string }>(items: T[], hide: boolean): T[] {
+	if (!hide) return items;
+	return items.filter((item) => !isDotfile(item.name));
+}
+
+/**
+ * Count the hidden items in an array. Callers use this to render
+ * an empty-state hint like "N hidden — show them?" so users don't
+ * get surprised by a mysteriously empty folder that actually contains
+ * dotfiles.
+ */
+export function countHidden<T extends { name: string }>(items: T[]): number {
+	let n = 0;
+	for (const item of items) if (isDotfile(item.name)) n++;
+	return n;
+}