feat: add --proxy flag for browser proxy configuration

[nmwcode]

Summary

Adds a --proxy flag to route all browser traffic through a proxy server.

Changes

• Add --proxy flag parsing in CLI (Rust)
• Parse proxy URLs with credentials (http://user:pass@host:port)
• Pass proxy config to Playwright's newContext()
• Add Zod validation for proxy schema

Usage

# Simple proxy
agent-browser --proxy http://proxy.com:8080 open example.com

# With authentication
agent-browser --proxy http://user:pass@proxy.com:8080 open example.com

Supports HTTP, HTTPS, and SOCKS5 protocols.

Background

Playwright requires proxy configuration at context creation time and does not respect HTTP_PROXY/HTTPS_PROXY environment variables.

Testing

Tested with authenticated and unauthenticated proxies. Verified IP changes using httpbin.org/ip.

[vercel]

@nmwcode is attempting to deploy a commit to the Vercel Labs Team on Vercel.

A member of the Team first needs to authorize it.

[ctate]

Thanks for adding proxy support - this is a useful feature!

A few things to address:

1. Proxy parsing edge case

As the bot mentioned, username-only proxies silently drop the username:

let Some(colon_pos) = creds.find(':') else {
  // Found @ but no : in credentials - return server without credentials
  let server_part = &rest[at_pos + 1..];
  return json!({ "server": format!("{}{}", protocol, server_part) });
};

For http://username@host:port, this returns just {"server": "http://host:port"} - the username is lost. Either preserve it or return an error explaining that password is required.

2. Missing tests

The parse_proxy() function should have unit tests covering:

• Basic proxy without auth: http://host:port
• Proxy with auth: http://user:pass@host:port
• Username only: http://user@host:port
• No protocol: host:port
• SOCKS5: socks5://host:port

3. Missing help output

Add --proxy to the help text in cli/src/output.rs so users can discover it.

[vercel]

Additional Suggestions:

1. The --proxy flag is not documented in the help output, preventing users from discovering this feature

2. The default_flags() test helper function is missing the proxy field, causing compilation errors when tests are run because the Flags struct now requires this field to be initialized

[nmwcode]

@ctate done!

[ctate]

Pulled this down, proxy flag works as expected. Nice addition.