fix: hide chat delete actions when the chat delete permission is disabled (#27714)

The chat delete endpoints gate on chat.delete for non-admins, but none of
the UI affordances that reach them were conditioned on it, so a user
without the permission is offered controls that always fail with
"Access prohibited".

Gates every entry point on the same condition the backend enforces,
matching the existing chat.share / chat.export / chat.import gates in the
same components:

- Sidebar chat menu (ChatMenu) Delete item — also covers the Search
  modal's menu, which reuses ChatMenu
- Sidebar Shift+hover inline Delete button (ChatItem)
- Sidebar hidden #delete-chat-button keyboard-shortcut target (ChatItem)
- Chat navbar menu Delete item (Navbar/Menu)
- Search modal Shift-held inline Delete button (SearchModal)
- Settings -> Data Controls -> Delete All Chats
- Settings -> Archived Chats per-row Delete

src/lib/components/layout/Navbar/Menu.svelte

@@ -487,16 +487,18 @@
 					<div class="flex items-center">{$i18n.t('Archive')}</div>
 				</button>
 
-				<button
-					draggable="false"
-					class="flex h-[1.6875rem] w-full items-center gap-2 rounded-xl px-2 text-[0.8125rem] cursor-pointer select-none hover:bg-gray-50/40 dark:hover:bg-gray-800/40"
-					on:click={() => {
-						deleteChatHandler();
-					}}
-				>
-					<GarbageBin className="size-3.5" strokeWidth="1.5" />
-					<div class="flex items-center">{$i18n.t('Delete')}</div>
-				</button>
+				{#if $user?.role === 'admin' || ($user?.permissions?.chat?.delete ?? true)}
+					<button
+						draggable="false"
+						class="flex h-[1.6875rem] w-full items-center gap-2 rounded-xl px-2 text-[0.8125rem] cursor-pointer select-none hover:bg-gray-50/40 dark:hover:bg-gray-800/40"
+						on:click={() => {
+							deleteChatHandler();
+						}}
+					>
+						<GarbageBin className="size-3.5" strokeWidth="1.5" />
+						<div class="flex items-center">{$i18n.t('Delete')}</div>
+					</button>
+				{/if}
 
 				<hr class="border-gray-50/30 dark:border-gray-800/30 mx-1 my-0.5" />