Add partnumber book snapshots for QuoteForge integration

- Migrations 026-028: qt_partnumber_books + qt_partnumber_book_items
  tables; is_primary_pn on lot_partnumbers; version VARCHAR(30);
  description VARCHAR(10000) on items (required by QuoteForge sync)
- Service: CreateSnapshot expands bundles, filters empty lot_name and
  ignored PNs, copies description, activates new book atomically,
  applies GFS retention (7d/5w/12m/10y) with explicit item deletion
- Task type TaskTypePartnumberBookCreate; handlers ListPartnumberBooks
  and CreatePartnumberBook; routes GET/POST /api/admin/pricing/partnumber-books
- UI: snapshot list + "Создать снапшот сопоставлений" button with
  progress polling on /vendor-mappings page
- Bible: history, api, background-tasks, vendor-mapping updated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

migrations/027_fix_partnumber_books_version_length.sql

@@ -0,0 +1,3 @@
+-- Fix version column length: PNBOOK-YYYY-MM-DD-NNN is 21 chars, VARCHAR(20) was too short.
+ALTER TABLE qt_partnumber_books
+    MODIFY COLUMN version VARCHAR(30) NOT NULL;