fix: reap zombie Chrome process and fast-detect crash for auto-restart (#1023)

When Chrome crashes (e.g. SIGTRAP from CHECK() assertion), the daemon
now:

1. Reaps the zombie immediately via a SIGCHLD handler in the event loop
   that calls waitpid(-1, WNOHANG)
2. Detects the crash instantly on the next command via a non-blocking
   try_wait() check (has_process_exited), avoiding the 3-second CDP
   timeout that is_connection_alive() would incur
3. Auto-relaunches Chrome transparently for the caller

Fixes #1017

Co-authored-by: ctate <366502+ctate@users.noreply.github.com>

cli/src/native/browser.rs

@@ -180,6 +180,14 @@ impl BrowserProcess {
             BrowserProcess::Lightpanda(p) => p.kill(),
         }
     }
+
+    /// Non-blocking check whether the browser process has exited.
+    pub fn has_exited(&mut self) -> bool {
+        match self {
+            BrowserProcess::Chrome(p) => p.has_exited(),
+            BrowserProcess::Lightpanda(_) => false,
+        }
+    }
 }
 
 pub struct BrowserManager {
@@ -643,6 +651,17 @@ impl BrowserManager {
         }
     }
 
+    /// Non-blocking check whether the locally-launched browser process has exited
+    /// (crashed or terminated). Also reaps the zombie if it has exited.
+    /// Returns false for external CDP connections (no child process to monitor).
+    pub fn has_process_exited(&mut self) -> bool {
+        if let Some(ref mut process) = self.browser_process {
+            process.has_exited()
+        } else {
+            false
+        }
+    }
+
     pub fn get_cdp_url(&self) -> &str {
         &self.ws_url
     }