Reading map: ring the newest highlight and the one quoted in the header

Two standing markers, drawn as rings rather than brighter dots. The animated
trace head is already a bright point and comes to rest on exactly the newest
node at the end of every draw cycle — under prefers-reduced-motion it parks
there permanently — so a second filled dot at that coordinate would read as a
rendering fault. Outlines say "different kind of thing" without competing.

The newest highlight is the LAST trace entry, never the max of `t`: the
payload is pre-sorted, `t` is date-only, and many highlights share a day.

The quoted one is looked up by text_hash, which /highlights/random now
returns beside the quote. The two fetches race on every page view, so the
hash is published both as a global and as a `garden:quote` event — one covers
each order. About one highlight in fifteen has no node, because its source
book was never indexed; markQuoted returns false and nothing is drawn.

Rings are flat geometry parented to the rotating world, so they are
billboarded each frame or they would vanish edge-on twice a revolution.

Also adds the "Currently reading" rail widget. It says how long ago on
purpose: six of the ten books on that shelf have not been opened in months,
and without a relative date the thing looks broken rather than honest. Past
45 days it mutes itself. No cover — kobo.books.isbn is a sideloader's UUID
for most of the shelf and storygraph_links has no cover URL.

The TOC rail is now always rendered, since it carries the widget too; it was
conditional on having two headings, which would have hidden the widget on the
homepage. Hidden explicitly on wide notebook pages, where a third grid child
would wrap under the sidebar.

src/env.d.ts

@@ -0,0 +1,18 @@
+/// <reference types="astro/client" />
+
+declare global {
+  interface Window {
+    /**
+     * `text_hash` of the reading highlight in the page header, set by Base.astro once
+     * api.c0smere.net/highlights/random answers. The reading map reads it to ring the node
+     * that passage came from.
+     *
+     * A global as well as a `garden:quote` event because the two fetches race: whichever
+     * lands second needs the other's result, and only one of the two mechanisms works in
+     * each order.
+     */
+    __gardenQuoteHash?: string;
+  }
+}
+
+export {};