fix: use AutoMigrate for new SQLite tables instead of hardcoded migrations

LocalPartnumberBook and LocalPartnumberBookItem added to AutoMigrate list
in localdb.go — consistent with all other local tables. Removed incorrectly
added addPartnumberBooks/addVendorSpecColumn functions from migrations.go
(vendor_spec column is handled by AutoMigrate via the LocalConfiguration model field).

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

internal/localdb/migrations.go

@@ -864,3 +864,4 @@ WHERE id IN (SELECT id FROM ranked)
 
 	return nil
 }
+