Seed: grade 3 rebuilt (every lesson 5+ questions, wrong figures/lesson text fixed), Persian digits and plain fractions across all grades, apply_fixups gains lesson/question_set, ledger save chunked for SQLite

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

CLAUDE.md

@@ -300,7 +300,7 @@ has been done before.
 ### Content
 
 - `content/seed/` is the whole curriculum and question bank as committed JSON: 10 grades (3–12), 5 subjects,
-  89 units, 1,145 islands, 5,406 lessons (every one has at least one question), 19,819 questions. `deploy.sh` runs `seed_content` on every release.
+  89 units, 1,145 islands, 5,406 lessons (every one has at least one question), 21,172 questions. `deploy.sh` runs `seed_content` on every release.
 - `seed_content` is idempotent, never deletes, and does not undo admin work: the `SeedRecord` ledger remembers
   what it delivered, so anything the admin deleted or renamed is not recreated; lesson text, `example`,
   `steps` and `figures` are only filled when empty. Questions bind to lessons **by title path**