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/files-app/_index.md

@@ -0,0 +1,16 @@
+---
+theme: files-app
+heading: "Files app — routing"
+kind: theme
+---
+
+**The URL model is done (2026-08-15).** The folder is the pathname —
+`/files/archive/Tests/platform/docs` — and `?view=` is a NAME within it, not a second copy of the path.
+Deep links and refresh work, which they never had. Landed across `559560de`, `98ba604a`, `7e31564c`,
+`0dc88b51`, `7359af2f`, with `files-route.ts` + 23 tests as the one owner of encoding and of which params
+belong to the overlay.
+
+Four bugs came out of that work and are fixed: closing a pane sent you home; `?view=` was stripped on
+every page load by a mount effect that had made deep links impossible since 2026-02-23; navigating kept a
+pane belonging to the folder you left; and the breadcrumb opted out of that last rule because it is a
+`<Link>` and never called the function enforcing it.