Add folder permissions UI and WebDAV protocol support

Permissions UI:
- FolderPermissionsDialog component with public/private toggle,
  role/user permission management, and access level badges
- Integrated into file manager toolbar (visible for folder admins)
- Backend returns accessLevel in folder detail endpoint

WebDAV server:
- Full WebDAV protocol at /webdav/ with Basic Auth (existing credentials)
- PROPFIND, GET, PUT, DELETE, MKCOL, COPY, MOVE, LOCK/UNLOCK support
- Permission-checked against existing folder access model
- In-memory lock stubs for Windows client compatibility
- 22 API integration tests covering all operations

Also fixes canAccess to check folder creator (was missing).

packages/admin/src/components/ui/switch.tsx

@@ -0,0 +1,33 @@
+import * as React from "react"
+import { Switch as SwitchPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Switch({
+  className,
+  size = "default",
+  ...props
+}: React.ComponentProps<typeof SwitchPrimitive.Root> & {
+  size?: "sm" | "default"
+}) {
+  return (
+    <SwitchPrimitive.Root
+      data-slot="switch"
+      data-size={size}
+      className={cn(
+        "peer group/switch inline-flex shrink-0 items-center rounded-full border border-transparent shadow-xs transition-all outline-none focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50 data-[size=default]:h-[1.15rem] data-[size=default]:w-8 data-[size=sm]:h-3.5 data-[size=sm]:w-6 data-[state=checked]:bg-primary data-[state=unchecked]:bg-input dark:data-[state=unchecked]:bg-input/80",
+        className
+      )}
+      {...props}
+    >
+      <SwitchPrimitive.Thumb
+        data-slot="switch-thumb"
+        className={cn(
+          "pointer-events-none block rounded-full bg-background ring-0 transition-transform group-data-[size=default]/switch:size-4 group-data-[size=sm]/switch:size-3 data-[state=checked]:translate-x-[calc(100%-2px)] data-[state=unchecked]:translate-x-0 dark:data-[state=checked]:bg-primary-foreground dark:data-[state=unchecked]:bg-foreground"
+        )}
+      />
+    </SwitchPrimitive.Root>
+  )
+}
+
+export { Switch }