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/archive/archive.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"io"
 	"log/slog"
 	"net/url"
 	"strings"
@@ -39,12 +38,6 @@ func (c Config) validate() Config {
 
 var DefaultConfig = Config{}
 
-func deferClose(cl io.Closer) {
-	if cl != nil {
-		_ = cl.Close()
-	}
-}
-
 // IsArchived checks if a url is archived.  It returns the archived url if it is archived, or an empty string if it is not.
 func (c Config) IsArchived(ctx context.Context, b extractor.Browser, target string) (extractor.Document, error) {
 	c = c.validate()