feature: add stealth mode, launch args, and init scripts to BrowserOptions

Add anti-bot-detection evasion support to reduce blocking by sites like
archive.ph. Stealth mode is enabled by default for all browsers and applies
common evasions: navigator.webdriver override, plugin/mimeType spoofing,
window.chrome stub, and outerWidth/outerHeight fixes. For Chromium,
--disable-blink-features=AutomationControlled is also added.

New BrowserOptions fields:
- Stealth *bool: toggle stealth presets (default true)
- LaunchArgs []string: custom browser launch arguments
- InitScripts []string: JavaScript injected before page scripts

Closes #56

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

stealth_test.go

@@ -0,0 +1,72 @@
+package extractor
+
+import (
+	"testing"
+)
+
+func TestMergeOptions_StealthDefault(t *testing.T) {
+	base := BrowserOptions{Stealth: Bool(true)}
+	got := mergeOptions(base, nil)
+	if got.Stealth == nil || !*got.Stealth {
+		t.Fatal("expected stealth to default to true")
+	}
+}
+
+func TestMergeOptions_StealthOverrideFalse(t *testing.T) {
+	base := BrowserOptions{Stealth: Bool(true)}
+	got := mergeOptions(base, []BrowserOptions{{Stealth: Bool(false)}})
+	if got.Stealth == nil || *got.Stealth {
+		t.Fatal("expected stealth to be overridden to false")
+	}
+}
+
+func TestMergeOptions_LaunchArgsAppend(t *testing.T) {
+	base := BrowserOptions{LaunchArgs: []string{"--arg1"}}
+	got := mergeOptions(base, []BrowserOptions{{LaunchArgs: []string{"--arg2", "--arg3"}}})
+	if len(got.LaunchArgs) != 3 {
+		t.Fatalf("expected 3 launch args, got %d", len(got.LaunchArgs))
+	}
+	if got.LaunchArgs[0] != "--arg1" || got.LaunchArgs[1] != "--arg2" || got.LaunchArgs[2] != "--arg3" {
+		t.Fatalf("unexpected launch args: %v", got.LaunchArgs)
+	}
+}
+
+func TestMergeOptions_InitScriptsAppend(t *testing.T) {
+	base := BrowserOptions{InitScripts: []string{"script1"}}
+	got := mergeOptions(base, []BrowserOptions{{InitScripts: []string{"script2"}}})
+	if len(got.InitScripts) != 2 {
+		t.Fatalf("expected 2 init scripts, got %d", len(got.InitScripts))
+	}
+	if got.InitScripts[0] != "script1" || got.InitScripts[1] != "script2" {
+		t.Fatalf("unexpected init scripts: %v", got.InitScripts)
+	}
+}
+
+func TestMergeOptions_StealthNilDoesNotOverride(t *testing.T) {
+	base := BrowserOptions{Stealth: Bool(true)}
+	got := mergeOptions(base, []BrowserOptions{{Stealth: nil}})
+	if got.Stealth == nil || !*got.Stealth {
+		t.Fatal("expected stealth to remain true when override is nil")
+	}
+}
+
+func TestStealthChromiumArgs(t *testing.T) {
+	if len(stealthChromiumArgs) == 0 {
+		t.Fatal("expected at least one chromium stealth arg")
+	}
+	found := false
+	for _, arg := range stealthChromiumArgs {
+		if arg == "--disable-blink-features=AutomationControlled" {
+			found = true
+		}
+	}
+	if !found {
+		t.Fatal("expected --disable-blink-features=AutomationControlled in stealth chromium args")
+	}
+}
+
+func TestStealthInitScripts(t *testing.T) {
+	if len(stealthInitScripts) == 0 {
+		t.Fatal("expected at least one stealth init script")
+	}
+}