fix: load balancer panics, stealth flag, shadow DOM polyfill

Fixes #1: replace unwrap() panics in run_multi_worker_serve with match on the Result.
Fixes #2: route /json round-robin via worker_port instead of hardcoded port+1.
Fixes #3: return 502 Bad Gateway when a worker is unreachable instead of silently dropping the connection.
Fixes #5: thread --stealth through start_with_options -> CdpContext -> BrowserContext::with_options so the flag actually has an effect in serve mode (was let _ before). Log message now reflects the actual capability based on the stealth cargo feature being compiled in.
Fixes #15: try/catch the parentNode assignment in the attachShadow polyfill so it doesn't throw a TypeError against the read-only Node.parentNode getter (Cloudflare Turnstile triggers this path).

crates/obscura-cdp/src/dispatch.rs

@@ -31,11 +31,19 @@ pub struct CdpContext {
 
 impl CdpContext {
     pub fn new() -> Self {
-        Self::new_with_proxy(None)
+        Self::new_with_options(None, false)
     }
 
     pub fn new_with_proxy(proxy: Option<String>) -> Self {
-        let default_context = Arc::new(BrowserContext::with_proxy("default".to_string(), proxy));
+        Self::new_with_options(proxy, false)
+    }
+
+    pub fn new_with_options(proxy: Option<String>, stealth: bool) -> Self {
+        let default_context = Arc::new(BrowserContext::with_options(
+            "default".to_string(),
+            proxy,
+            stealth,
+        ));
         CdpContext {
             pages: Vec::new(),
             sessions: HashMap::new(),