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/transmission/_index.md

@@ -0,0 +1,13 @@
+---
+theme: transmission
+heading: "Transmission"
+kind: theme
+---
+
+Phase 1 (parity with `_references/transmission-web`) shipped 2026-07-30: the `officer-transmission`
+sidecar plus `/transmission` (torrents / stats / settings). Everything below is **phase 2** — none of
+it exists in the reference app, so none of it was in scope for parity.
+
+### Probably needed regardless
+
+### Ideas, unprioritised