refactor: restructure API, deduplicate code, expand test coverage

- Extract shared DeferClose helper, removing 14 duplicate copies
- Rename PlayWright-prefixed types to cleaner names (BrowserOptions,
  BrowserSelection, NewBrowser, etc.)
- Rename fields: ServerAddress, RequireServer (was DontLaunchOnConnectFailure)
- Extract shared initBrowser/mergeOptions into browser_init.go,
  deduplicating ~120 lines between NewBrowser and NewInteractiveBrowser
- Remove unused locator field from document struct
- Add tests for all previously untested packages (archive, aislegopher,
  wegmans, useragents, powerball) and expand existing test suites
- Add MIGRATION.md documenting all breaking API changes

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

sites/wegmans/wegmans_test.go

@@ -0,0 +1,39 @@
+package wegmans
+
+import (
+	"context"
+	"net/url"
+	"testing"
+)
+
+func TestGetItemPrice_NilBrowser(t *testing.T) {
+	u, _ := url.Parse("https://shop.wegmans.com/product/24921")
+	_, err := DefaultConfig.GetItemPrice(context.Background(), nil, u)
+	if err != ErrNilBrowser {
+		t.Errorf("expected ErrNilBrowser, got %v", err)
+	}
+}
+
+func TestGetItemPrice_NilURL(t *testing.T) {
+	// NilBrowser check comes before NilURL, so we can't test NilURL
+	// independently without a real browser. Verify the error sentinel exists.
+	if ErrNilURL.Error() != "url is nil" {
+		t.Errorf("ErrNilURL = %q, want %q", ErrNilURL.Error(), "url is nil")
+	}
+}
+
+func TestGetItemPrice_ErrorSentinels(t *testing.T) {
+	if ErrInvalidURL.Error() != "invalid url" {
+		t.Errorf("ErrInvalidURL = %q, want %q", ErrInvalidURL.Error(), "invalid url")
+	}
+	if ErrNilBrowser.Error() != "browser is nil" {
+		t.Errorf("ErrNilBrowser = %q, want %q", ErrNilBrowser.Error(), "browser is nil")
+	}
+}
+
+func TestItem_ZeroValue(t *testing.T) {
+	var item Item
+	if item.ID != 0 || item.Name != "" || item.Price != 0 || item.UnitPrice != 0 || item.Unit != "" {
+		t.Error("zero-value Item should have empty/zero fields")
+	}
+}