enhance: thread-safe CookieJar, SameSite cookie attr, dynamic Google countries

- Wrap staticCookieJar in struct with sync.RWMutex for thread safety
- Add SameSite field to Cookie struct with Strict/Lax/None constants
- Update Playwright cookie conversion functions for SameSite
- Replace hardcoded 4-country switch with dynamic country code generation

Closes #20, #22, #23
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

playwright.go

@@ -72,8 +72,37 @@ type BrowserOptions struct {
 	UseLocalOnly bool
 }
 
+func sameSiteToPlaywright(s SameSite) *playwright.SameSiteAttribute {
+	switch s {
+	case SameSiteStrict:
+		return playwright.SameSiteAttributeStrict
+	case SameSiteLax:
+		return playwright.SameSiteAttributeLax
+	case SameSiteNone:
+		return playwright.SameSiteAttributeNone
+	default:
+		return nil
+	}
+}
+
+func playwrightSameSiteToSameSite(s *playwright.SameSiteAttribute) SameSite {
+	if s == nil {
+		return ""
+	}
+	switch *s {
+	case *playwright.SameSiteAttributeStrict:
+		return SameSiteStrict
+	case *playwright.SameSiteAttributeLax:
+		return SameSiteLax
+	case *playwright.SameSiteAttributeNone:
+		return SameSiteNone
+	default:
+		return ""
+	}
+}
+
 func cookieToPlaywrightOptionalCookie(cookie Cookie) playwright.OptionalCookie {
-	return playwright.OptionalCookie{
+	oc := playwright.OptionalCookie{
 		Name:     cookie.Name,
 		Value:    cookie.Value,
 		Domain:   playwright.String(cookie.Host),
@@ -81,6 +110,10 @@ func cookieToPlaywrightOptionalCookie(cookie Cookie) playwright.OptionalCookie {
 		Expires:  playwright.Float(float64(cookie.Expires.Unix())),
 		HttpOnly: playwright.Bool(cookie.HttpOnly),
 	}
+	if cookie.SameSite != "" {
+		oc.SameSite = sameSiteToPlaywright(cookie.SameSite)
+	}
+	return oc
 }
 
 func playwrightCookieToCookie(cookie playwright.Cookie) Cookie {
@@ -91,6 +124,7 @@ func playwrightCookieToCookie(cookie playwright.Cookie) Cookie {
 		Path:     cookie.Path,
 		Expires:  time.Unix(int64(cookie.Expires), 0),
 		HttpOnly: cookie.HttpOnly,
+		SameSite: playwrightSameSiteToSameSite(cookie.SameSite),
 	}
 }