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/aislegopher/aislegopher.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"io"
 	"net/url"
 	"strconv"
 	"strings"
@@ -27,11 +26,6 @@ type Item struct {
 	Price float64
 }
 
-func deferClose(cl io.Closer) {
-	if cl != nil {
-		_ = cl.Close()
-	}
-}
 func GetItemFromURL(ctx context.Context, b extractor.Browser, u *url.URL) (Item, error) {
 	return DefaultConfig.GetItemFromURL(ctx, b, u)
 }
@@ -57,7 +51,7 @@ func (c Config) GetItemFromURL(ctx context.Context, b extractor.Browser, u *url.
 	res.ID, _ = strconv.Atoi(a[3])
 
 	doc, err := b.Open(ctx, u.String(), extractor.OpenPageOptions{})
-	defer deferClose(doc)
+	defer extractor.DeferClose(doc)
 	if err != nil {
 		return res, fmt.Errorf("failed to open page: %w", err)
 	}