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

crates/worker/Cargo.toml

@@ -29,3 +29,4 @@ tracing           = { workspace = true }
 tracing-subscriber = { workspace = true }
 dotenvy           = { workspace = true }
 async-trait       = { workspace = true }
+chrono            = { workspace = true }