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)/page.tsx

@@ -1,16 +1,35 @@
 "use client"
 
 import { useMemo } from "react"
+import { useQueryClient } from "@tanstack/react-query"
 import { useTimeline, useDateSummary } from "@/hooks/use-timeline"
 import { groupByDate } from "@/lib/timeline"
 import { PhotoGrid } from "@/components/photo-grid"
 import { DateScrubber } from "@/components/date-scrubber"
+import api from "@/lib/api"
+import { toast } from "sonner"
 
 export default function TimelinePage() {
+  const qc = useQueryClient()
   const { assets, isLoading, hasMore, loadMore, total } = useTimeline()
   const { data: dateSummary } = useDateSummary()
   const groups = useMemo(() => groupByDate(assets), [assets])
 
+  const handleDeleteAssets = async (ids: string[]) => {
+    let deleted = 0
+    for (const id of ids) {
+      try {
+        await api.delete(`/assets/${id}`)
+        deleted++
+      } catch { /* skip */ }
+    }
+    if (deleted > 0) {
+      toast.success(`Deleted ${deleted} photo(s)`)
+      qc.invalidateQueries({ queryKey: ["timeline"] })
+      qc.invalidateQueries({ queryKey: ["date-summary"] })
+    }
+  }
+
   return (
     <div className="flex flex-col gap-4">
       <div className="flex items-center justify-between">
@@ -27,6 +46,7 @@ export default function TimelinePage() {
           isLoading={isLoading}
           hasMore={hasMore}
           onLoadMore={() => loadMore()}
+          onDeleteAssets={handleDeleteAssets}
         />
         <DateScrubber dates={dateSummary ?? []} />
       </div>