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>

article_test.go

@@ -0,0 +1,29 @@
+package extractor
+
+import "testing"
+
+func TestArticle_ZeroValue(t *testing.T) {
+	var a Article
+	if a.Title != "" || a.Content != "" || a.Length != 0 {
+		t.Error("zero-value Article should have empty fields")
+	}
+}
+
+func TestArticle_FieldAssignment(t *testing.T) {
+	a := Article{
+		Title:       "Test Title",
+		Content:     "<p>hello</p>",
+		TextContent: "hello",
+		Length:      5,
+		Excerpt:     "hello",
+		Byline:      "Author",
+		SiteName:    "Example",
+		Lang:        "en",
+	}
+	if a.Title != "Test Title" {
+		t.Errorf("Title = %q, want %q", a.Title, "Test Title")
+	}
+	if a.Length != 5 {
+		t.Errorf("Length = %d, want 5", a.Length)
+	}
+}