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.go

@@ -0,0 +1,50 @@
+package extractor
+
+// stealthChromiumArgs are launch arguments that reduce automation detection for Chromium-based browsers.
+var stealthChromiumArgs = []string{
+	"--disable-blink-features=AutomationControlled",
+}
+
+// stealthInitScripts are JavaScript snippets injected before page scripts to mask automation signals.
+var stealthInitScripts = []string{
+	// Override navigator.webdriver to return undefined (the real-browser value).
+	`Object.defineProperty(navigator, 'webdriver', {get: () => undefined})`,
+
+	// Populate navigator.plugins with a realistic entry so plugins.length > 0.
+	`Object.defineProperty(navigator, 'plugins', {
+		get: () => {
+			const arr = [
+				{ name: 'PDF Viewer', filename: 'internal-pdf-viewer', description: 'Portable Document Format' },
+				{ name: 'Chrome PDF Plugin', filename: 'internal-pdf-viewer', description: '' },
+				{ name: 'Chromium PDF Viewer', filename: 'internal-pdf-viewer', description: '' },
+			];
+			arr.item = (i) => arr[i] || null;
+			arr.namedItem = (n) => arr.find(p => p.name === n) || null;
+			arr.refresh = () => {};
+			return arr;
+		},
+	})`,
+
+	// Populate navigator.mimeTypes to match the fake plugins above.
+	`Object.defineProperty(navigator, 'mimeTypes', {
+		get: () => {
+			const arr = [
+				{ type: 'application/pdf', suffixes: 'pdf', description: 'Portable Document Format' },
+			];
+			arr.item = (i) => arr[i] || null;
+			arr.namedItem = (n) => arr.find(m => m.type === n) || null;
+			return arr;
+		},
+	})`,
+
+	// Provide window.chrome runtime stub (Chromium-only signal; harmless on other engines).
+	`if (!window.chrome) {
+		window.chrome = { runtime: {} };
+	}`,
+
+	// Fix outerWidth/outerHeight which are 0 in headless mode.
+	`if (window.outerWidth === 0) {
+		Object.defineProperty(window, 'outerWidth',  { get: () => window.innerWidth  });
+		Object.defineProperty(window, 'outerHeight', { get: () => window.innerHeight });
+	}`,
+}