feat(core): YouTube playlist/channel/YTM-playlist capture with parent–child entries

- ytdlp: add fetch_playlist_info() using yt-dlp -J --flat-playlist for
  reliable container title + shallow entry list; normalize item URLs via
  webpage_url → absolute url → id fallback (domain inferred from container
  URL so YTM stays on music.youtube.com)
- capture: add record_container_entry() (no blob, no primary_media artifact);
  extend record_media_entry() with parent_entry_id/root_entry_id params (all
  existing single-item call sites pass None, None)
- capture: implement YouTubePlaylist / YouTubeChannel / YouTubeMusicPlaylist
  capture path replacing the two not-implemented stubs: fetch playlist info →
  create container entry (reusing existing run + item) → per-child run items
  (parent_item_id = container item) → download each video/track as a child
  entry; per-child failures are non-fatal; perform_capture returns result.status
  reflecting actual run outcome so capture_handler marks the job correctly
- archive: add child_count i64 to EntrySummary (col 12 in all listing queries);
  add get_entry_summary() private helper; fix get_entry_detail() to use
  get_entry_summary() so child entries are resolvable via the detail endpoint;
  add list_child_entries(conn, uid, caller_bits) with the same
  admin/collection visibility predicate as list_root_entries

archive_runs.requested_count stays 1 (one user locator); discovered/
completed/failed_count reflect container item + N video items via
refresh_run_counters.

.gitignore

@@ -7,6 +7,8 @@
 !docs/
 !docs/LICENSE
 !docs/README*
+!docs/superpowers/
+!docs/superpowers/**
 !crates
 !crates/**