feat: add connect command for persistent CDP sessions (#127)

Adds a `connect <port>` command that establishes a CDP connection
to a running browser. The daemon remembers the connection, so
subsequent commands work without needing --cdp on every call.

Example:
  agent-browser connect 9222
  agent-browser snapshot  # works without --cdp
  agent-browser tab
  agent-browser close

cli/src/output.rs

@@ -1261,6 +1261,7 @@ Core Commands:
   pdf <path>                 Save as PDF
   snapshot                   Accessibility tree with refs (for AI)
   eval <js>                  Run JavaScript
+  connect <port>             Connect to browser via CDP (e.g., connect 9222)
   close                      Close browser
 
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