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/duckduckgo/duckduckgo.go

@@ -3,7 +3,6 @@ package duckduckgo
 import (
 	"context"
 	"fmt"
-	"io"
 	"log/slog"
 	"net/url"
 
@@ -71,12 +70,6 @@ type Result struct {
 	Description string
 }
 
-func deferClose(cl io.Closer) {
-	if cl != nil {
-		_ = cl.Close()
-	}
-}
-
 func (c Config) OpenSearch(ctx context.Context, b extractor.Browser, query string) (SearchPage, error) {
 	u := c.ToSearchURL(query)
 
@@ -97,7 +90,7 @@ func (c Config) Search(ctx context.Context, b extractor.Browser, query string) (
 
 	slog.Info("searching", "url", u, "query", query, "config", c, "browser", b)
 	doc, err := b.Open(ctx, u.String(), extractor.OpenPageOptions{})
-	defer deferClose(doc)
+	defer extractor.DeferClose(doc)
 
 	if err != nil {
 		return nil, fmt.Errorf("failed to open url: %w", err)