todo: one file per item, grouped by theme, with a generated index

TODO.md had reached 1050 lines and 72 open items across 28 sections, read mostly
on a phone. It is now a directory: todo/<theme>/<item>.md, one card per file, with
frontmatter carrying id, status, created date and order, and the prose body copied
across verbatim. TODO.md becomes a generated index (bun run todo:index).

Dates: where an item's prose stated one it is used; otherwise its old section's;
otherwise 2026-08-20, floored at the day before the split rather than invented.
date_source records which.

Shaped for a two-way Kanban board, filed as todo/tooling — a card is a file, id is
the identity, frontmatter is the machine's half and the body is the owner's.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

todo/multi-user/the-music-library-is-one-global-index.md

@@ -0,0 +1,13 @@
+---
+id: multi-user/the-music-library-is-one-global-index
+title: "The music library is one global index"
+theme: multi-user
+status: open
+created: 2026-08-20
+date_source: assumed
+order: 17
+---
+
+**The music library is one global index.** `sidecar/music/indexer.ts` reads `HOME_DIR` and serves
+every account from it. Favourites, playlists and now-playing _are_ per-user. Deliberate for now
+(one household, one library) but worth stating rather than discovering.