feat: add dialog detection and document dialog commands (#999)

Fixes #992

When a JavaScript dialog (alert/confirm/prompt) blocks the page, agents
had no way to detect it — all commands just timed out with generic errors.

- Add `dialog status` command to check for pending dialogs
- Track dialog state via CDP Page.javascriptDialogOpening/Closed events
- Auto-inject `warning` field into all command responses when a dialog is
  pending, so agents can distinguish dialog-blocked timeouts from other issues
- Document dialog commands in SKILL.md (was missing entirely), README.md,
  docs site, and --help output

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

cli/src/output.rs

@@ -122,6 +122,7 @@ pub fn print_response_with_opts(resp: &Response, action: Option<&str>, opts: &Ou
         } else {
             println!("{}", serde_json::to_string(resp).unwrap_or_default());
         }
+        // JSON mode includes the warning field in the JSON payload already
         return;
     }
 
@@ -131,10 +132,42 @@ pub fn print_response_with_opts(resp: &Response, action: Option<&str>, opts: &Ou
             color::error_indicator(),
             resp.error.as_deref().unwrap_or("Unknown error")
         );
+        // Still print dialog warning after errors, since a pending dialog
+        // is the most common cause of commands timing out
+        if let Some(ref warning) = resp.warning {
+            eprintln!("{} {}", color::warning_indicator(), warning);
+        }
         return;
     }
 
     if let Some(data) = &resp.data {
+        // Dialog status response
+        if action == Some("dialog") {
+            if let Some(has_dialog) = data.get("hasDialog").and_then(|v| v.as_bool()) {
+                if has_dialog {
+                    let dtype = data
+                        .get("type")
+                        .and_then(|v| v.as_str())
+                        .unwrap_or("unknown");
+                    let message = data.get("message").and_then(|v| v.as_str()).unwrap_or("");
+                    println!(
+                        "{} JavaScript {} dialog is open: \"{}\"",
+                        color::warning_indicator(),
+                        dtype,
+                        message
+                    );
+                    if let Some(default_prompt) = data.get("defaultPrompt").and_then(|v| v.as_str())
+                    {
+                        println!("  Default prompt text: \"{}\"", default_prompt);
+                    }
+                    println!("  Use `dialog accept [text]` or `dialog dismiss` to resolve it");
+                } else {
+                    println!("{} No dialog is currently open", color::success_indicator());
+                }
+                print_warning(resp);
+                return;
+            }
+        }
         if action == Some("storage_get") {
             if let Some(output) = format_storage_text(data) {
                 println!("{}", output);
@@ -888,6 +921,14 @@ pub fn print_response_with_opts(resp: &Response, action: Option<&str>, opts: &Ou
         // Default success
         println!("{} Done", color::success_indicator());
     }
+
+    print_warning(resp);
+}
+
+fn print_warning(resp: &Response) {
+    if let Some(ref warning) = resp.warning {
+        eprintln!("{} {}", color::warning_indicator(), warning);
+    }
 }
 
 /// Print command-specific help. Returns true if help was printed, false if command unknown.
@@ -1995,13 +2036,14 @@ Examples:
             r##"
 agent-browser dialog - Handle browser dialogs
 
-Usage: agent-browser dialog <response> [text]
+Usage: agent-browser dialog <accept|dismiss|status> [text]
 
-Respond to browser dialogs (alert, confirm, prompt).
+Respond to or check for browser dialogs (alert, confirm, prompt).
 
 Operations:
   accept [text]        Accept dialog, optionally with prompt text
   dismiss              Dismiss/cancel dialog
+  status               Check if a dialog is currently open
 
 Global Options:
   --json               Output as JSON
@@ -2011,6 +2053,7 @@ Examples:
   agent-browser dialog accept
   agent-browser dialog accept "my input"
   agent-browser dialog dismiss
+  agent-browser dialog status
 "##
         }