Reading map: correct the measured no-op rate for markQuoted

0.9% (2 of 230), not the ~7% estimated before the endpoint was restricted to
indexed books — that filter, added for the byline fix, removed nearly every
orphan as a side effect.

src/lib/reading-map.js

@@ -408,10 +408,11 @@ export function build(container, data) {
      * Ring the node a quoted passage came from. `textHash` is the `text_hash` that
      * api.c0smere.net/highlights/random returns beside the quote.
      *
-     * Returns false when that passage has no node — about 1 highlight in 15, because its
-     * source book has never been indexed into library-rag and so was never placed. That is a
-     * normal outcome, not an error: the caller does nothing and the map simply shows no ring.
-     * The set shrinks as those sources get indexed.
+     * Returns false when that passage has no node. Measured at 2 of the 230 quotes the header
+     * can draw (0.9%) — the endpoint already restricts itself to books library-rag has
+     * indexed, so the only survivors are passages the export could not confirm inside the
+     * chunk they claim. A normal outcome, not an error: the caller does nothing and no ring
+     * is drawn.
      */
     markQuoted(textHash) {
       const node = nodeOfHash.get(textHash);