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/localdb.go

@@ -142,6 +142,8 @@ func New(dbPath string) (*LocalDB, error) {
 		&LocalRemoteMigrationApplied{},
 		&LocalSyncGuardState{},
 		&PendingChange{},
+		&LocalPartnumberBook{},
+		&LocalPartnumberBookItem{},
 	); err != nil {
 		return nil, fmt.Errorf("migrating sqlite database: %w", err)
 	}

internal/localdb/migrations.go

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