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)/trash/page.tsx

@@ -0,0 +1,87 @@
+"use client"
+
+import { useEffect, useState } from "react"
+import { useQuery, useQueryClient, useMutation } from "@tanstack/react-query"
+import api from "@/lib/api"
+import type { TimelineResponse, AssetResponse } from "@/lib/types"
+import { PhotoCard } from "@/components/photo-card"
+import { Button } from "@/components/ui/button"
+import { Spinner } from "@/components/ui/spinner"
+import { toast } from "sonner"
+import { RotateCcwIcon } from "lucide-react"
+
+export default function TrashPage() {
+  const qc = useQueryClient()
+
+  const { data, isLoading } = useQuery({
+    queryKey: ["trash"],
+    queryFn: async () => {
+      const { data } = await api.get<TimelineResponse>("/assets/trash", {
+        params: { limit: 100, offset: 0 },
+      })
+      return data
+    },
+  })
+
+  const restore = useMutation({
+    mutationFn: async (assetId: string) => {
+      await api.post(`/assets/${assetId}/restore`)
+    },
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ["trash"] })
+      qc.invalidateQueries({ queryKey: ["timeline"] })
+      qc.invalidateQueries({ queryKey: ["date-summary"] })
+    },
+  })
+
+  const assets = data?.assets ?? []
+
+  return (
+    <div className="flex flex-col gap-4">
+      <div className="flex items-center justify-between">
+        <h1 className="text-lg font-semibold">Trash</h1>
+        {data && data.total > 0 && (
+          <span className="text-sm text-muted-foreground">
+            {data.total} items
+          </span>
+        )}
+      </div>
+
+      {isLoading ? (
+        <Spinner />
+      ) : assets.length === 0 ? (
+        <p className="py-12 text-center text-muted-foreground">
+          Trash is empty
+        </p>
+      ) : (
+        <div className="grid grid-cols-2 gap-1 sm:grid-cols-3 md:grid-cols-4 lg:grid-cols-5 xl:grid-cols-6">
+          {assets.map((asset) => (
+            <div key={asset.id} className="group relative">
+              <div className="opacity-60">
+                <PhotoCard asset={asset} />
+              </div>
+              <div className="absolute top-1.5 right-1.5 opacity-0 group-hover:opacity-100">
+                <Button
+                  size="icon"
+                  variant="secondary"
+                  className="h-7 w-7"
+                  disabled={restore.isPending}
+                  onClick={async () => {
+                    try {
+                      await restore.mutateAsync(asset.id)
+                      toast.success("Photo restored")
+                    } catch {
+                      toast.error("Failed to restore")
+                    }
+                  }}
+                >
+                  <RotateCcwIcon className="h-3.5 w-3.5" />
+                </Button>
+              </div>
+            </div>
+          ))}
+        </div>
+      )}
+    </div>
+  )
+}