feat: safe deletion, album/asset delete, trash, README update

- volume-aware deletion: read-only volumes remove DB only, writable
  volumes soft-delete to trash with configurable grace period
- trash page with restore, worker purge sweep (TRASH_RETENTION_DAYS)
- album delete endpoint + sidebar trash icon
- asset delete from timeline selection toolbar
- all listing queries exclude trashed assets (deleted_at IS NULL)
- timeline ordered by EXIF capture date, date-summary endpoint
- README rewritten with features, setup, full env var table

k-photos-frontend/app/(app)/layout.tsx

@@ -16,7 +16,7 @@ import { AlbumSidebar } from "@/components/album-sidebar"
 import { AdminSidebar } from "@/components/admin-sidebar"
 import { UploadDialog } from "@/components/upload-dialog"
 import { Spinner } from "@/components/ui/spinner"
-import { CameraIcon, LogOutIcon } from "lucide-react"
+import { CameraIcon, LogOutIcon, Trash2Icon } from "lucide-react"
 import { Button } from "@/components/ui/button"
 import Link from "next/link"
 
@@ -53,13 +53,22 @@ export default function AppLayout({ children }: { children: React.ReactNode }) {
           <AlbumSidebar />
           <AdminSidebar />
         </SidebarContent>
-        <div className="flex items-center justify-between border-t px-4 py-2">
-          <span className="truncate text-xs text-muted-foreground">
-            {user?.username}
-          </span>
-          <Button variant="ghost" size="icon" className="h-7 w-7" onClick={logout}>
-            <LogOutIcon className="h-3.5 w-3.5" />
-          </Button>
+        <div className="flex flex-col border-t">
+          <Link
+            href="/trash"
+            className="flex items-center gap-2 px-4 py-2 text-xs text-muted-foreground hover:text-foreground"
+          >
+            <Trash2Icon className="h-3.5 w-3.5" />
+            Trash
+          </Link>
+          <div className="flex items-center justify-between px-4 py-2">
+            <span className="truncate text-xs text-muted-foreground">
+              {user?.username}
+            </span>
+            <Button variant="ghost" size="icon" className="h-7 w-7" onClick={logout}>
+              <LogOutIcon className="h-3.5 w-3.5" />
+            </Button>
+          </div>
         </div>
       </Sidebar>
       <SidebarInset>