Connect reading plans to study/audio, cache offline audio, add journal export

Reading plan days now offer "Study this" (seeds a new chunk-builder project
with the day's full passage and jumps straight into the Study editor) and
"Listen" (starts book-mode audio at the right chapter via a new
handlePlayBookAudioFrom, avoiding a stale-closure bug the reader-state
approach would hit). Fixed the "Listen to BSB Audio" player only rendering
when a study project existed, leaving Listen with nowhere to show up.

The service worker now caches audio.bible.helloao.org (the actual host
serving narrator audio, not just the text/cross-ref API) and no longer
tries to cache 206 Partial Content responses, which the Cache API rejects
and was throwing unhandled rejections for every range-requested audio file.

Added a reading journal export (Settings > My reading journal): gathers
bookmarks, text highlights, and completed plans, fetches their verse text,
and offers a .docx download or a print-to-PDF page.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/hooks/useAudio.js

@@ -67,6 +67,20 @@ export function useAudio(readerBookAbbrev, readerChapter) {
     }
   };
 
+  // Starts book-mode playback at an arbitrary chapter (e.g. a reading plan's
+  // "today" chapter) instead of always chapter 1. Explicit args avoid relying
+  // on reader state that may not have re-rendered yet if called right after
+  // navigating there in the same event handler.
+  const handlePlayBookAudioFrom = async (abbrev, startChapter) => {
+    audioModeRef.current = 'book';
+    setAudioBook(abbrev);
+    try {
+      await playAudioChapter(abbrev, startChapter, audioNarrator);
+    } catch {
+      setAudioState({ status: 'error', chapter: 0, total: 0 });
+    }
+  };
+
   const handleStopBookAudio = () => {
     if (audioRef.current) {
       audioRef.current.pause();
@@ -161,6 +175,7 @@ export function useAudio(readerBookAbbrev, readerChapter) {
     audioState,
     audioProgress,
     handlePlayBookAudio,
+    handlePlayBookAudioFrom,
     handleStopBookAudio,
     handleToggleBookAudioPause,
     handleSkipBookChapter,