Teaching tools: word occurrences, blanks handout, templates, series progress, book info, comments

- Words tab: "Where else" lists every verse using a Strong's number, by book
  (new /api/strongs/:number/occurrences, indexed from the interlinear files)
- Handout: fill-in-the-blanks layout with a word bank
- Four new study templates: character, topical, word, verse by verse
- Finish: series progress (not started / studied / ready / taught)
- Background: book at a glance for all 66 books
- Chunk comments for co-teachers, merged between copies
- TODO: correct BSB audio note, tick co-teacher comments

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

TODO.md

@@ -15,7 +15,8 @@ Ideas for the app that haven't been built yet, roughly in the order I'd do them.
 - [x] **Split `server/index.js`** into one file per area (`server/routes/`: auth, account, projects, reader, sharing, admin).
 
 ## Teaching together
-- [ ] **Comments between co-teachers.** Notes on a chunk addressed to the other person, instead of editing each other's text.
+- [x] **Comments between co-teachers.** Comments on a chunk (under "More"), merged between copies and ticked off when dealt with.
+      Still to do: address a comment to one person, and notify them.
 - [ ] **Live updates and "who's here".** A co-teacher's changes appear within seconds, with a marker like "Sam is on chunk 3"
       (server-sent events or short polling). Today changes arrive when the tab regains focus or every couple of minutes.
 - [ ] **Ask Claude inside the app.** Draft discussion questions, tighten an outline point, summarise notes, using the owner's own
@@ -23,7 +24,7 @@ Ideas for the app that haven't been built yet, roughly in the order I'd do them.
 
 ## Reading
 - [ ] **Read-aloud with highlighting.** The device's voice reads the chapter and the verse being read is highlighted; useful for
-      the BSB and NET, which have no audio.
+      the NET and other translations that have no matching audio (the BSB and ESV already have narration).
 - [x] **Cross-reference map.** A picture of the links between chapters, from IQ Bible's reference graph (needs the IQ Bible key).
 
 ## Decided against, for now