fix: randomize hardware fingerprint values across browser sessions

Replace static stealthChromiumScripts and stealthFirefoxScripts slices
with builder functions that accept hardware profile structs. Each browser
session now randomly selects from a pool of 6 realistic profiles per
engine, and Chromium connection stats receive per-session jitter (±20ms
RTT, ±2 Mbps downlink). This prevents anti-bot systems from correlating
sessions via identical WebGL, connection, mozInnerScreen, and
hardwareConcurrency fingerprints.

Closes #71

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

browser_init.go

@@ -74,9 +74,9 @@ func initBrowser(opt BrowserOptions) (*browserInitResult, error) {
 		initScripts = append(initScripts, stealthCommonScripts...)
 		switch opt.Browser {
 		case BrowserChromium:
-			initScripts = append(initScripts, stealthChromiumScripts...)
+			initScripts = append(initScripts, buildChromiumStealthScripts(randomChromiumProfile())...)
 		case BrowserFirefox:
-			initScripts = append(initScripts, stealthFirefoxScripts...)
+			initScripts = append(initScripts, buildFirefoxStealthScripts(randomFirefoxProfile())...)
 		}
 	}