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/headscale/acl-policy.md

@@ -0,0 +1,17 @@
+---
+id: headscale/acl-policy
+title: "ACL policy"
+theme: headscale
+status: done
+created: 2026-08-20
+date_source: assumed
+order: 1
+---
+
+**ACL policy.** `/api/v1/policy` GET/PUT behind `/_officer/policy`, with a plain HuJSON textarea
+that sends the text byte for byte and shows headscale's verdict verbatim (line and column
+included). Officer does not pre-validate: headscale owns the only parser that resolves groups,
+tags and hosts, and a second weaker one would disagree with the thing that actually enforces.
+**The mode cannot be read.** A file-backed policy is still served over GET; only a PUT refuses,
+with "update is disabled for modes other than 'database'". So the first save is what discovers
+writability, and a refusal becomes a persistent read-only banner. Verified live, not inferred.