feat: support remote CDP WebSocket URLs in --cdp flag (#99)

Previously, the --cdp flag only accepted a port number and connected via
http://localhost:{port}. This made it impossible to connect to remote
browser services like Kernel, Browserless, etc. that provide WebSocket URLs.

The --cdp flag now accepts either:
- A port number (e.g., 9222) for local connections
- A full WebSocket URL (e.g., wss://...) for remote browser services

Changes:
- Added cdpUrl field to LaunchCommand type
- Updated protocol validation to accept URL format with scheme validation
- Modified connectViaCDP to detect and handle both formats
- Handle numeric strings for JSON serialization edge cases
- Updated CLI to send cdpUrl or cdpPort based on input format
- Updated README with examples for remote connections

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -476,8 +476,15 @@ agent-browser close
 
 # Or pass --cdp on each command
 agent-browser --cdp 9222 snapshot
+
+# Connect to remote browser via WebSocket URL
+agent-browser --cdp "wss://your-browser-service.com/cdp?token=..." snapshot
 ```
 
+The `--cdp` flag accepts either:
+- A port number (e.g., `9222`) for local connections via `http://localhost:{port}`
+- A full WebSocket URL (e.g., `wss://...` or `ws://...`) for remote browser services
+
 This enables control of:
 - Electron apps
 - Chrome/Chromium instances with remote debugging