feat: add --proxy flag for browser proxy configuration (#16)

* feat: add --proxy flag for browser proxy support

Add CLI flag to configure HTTP/SOCKS proxy for Playwright browser context.
Supports URL format with optional credentials: http://user:pass@host:port

* fix: improve proxy parsing error handling

- Handle malformed credentials (@ without :) by ignoring incomplete creds
- Replace unwrap() with expect() for better error messages
- Addresses Vercel bot code review suggestions

* Restaura cambios locales: soporte AGENT_BROWSER_HOME y timeout aumentado

- Agrega soporte para variable de entorno AGENT_BROWSER_HOME en connection.rs
- Aumenta timeout por defecto de 10s a 60s para conexiones más lentas

* feat: add --proxy flag for browser proxy configuration

Implements proxy support based on PR #16 with reviewer feedback:

Features:
- Parse proxy URLs: http://[user:pass@]host:port
- Support for HTTP, HTTPS, and SOCKS5 protocols
- Handle username-only auth (preserves username with empty password)
- Apply proxy to both standard and persistent contexts

Changes:
- cli/src/flags.rs: Add proxy flag parsing
- cli/src/main.rs: Add parse_proxy() with comprehensive tests
- cli/src/output.rs: Add --proxy to help output
- cli/src/commands.rs: Fix test helper to include proxy field
- src/types.ts: Add proxy to LaunchCommand interface
- src/protocol.ts: Add proxy validation schema
- src/browser.ts: Apply proxy to context creation

Tests:
- 7 unit tests for parse_proxy() covering all edge cases
- All Rust tests passing (69 tests)
- All TypeScript tests passing (168 tests)
- TypeScript typecheck passing

Resolves feedback from PR #16:
- Fixed username-only proxy handling (issue #2681046975)
- Added comprehensive unit tests
- Added --proxy to help documentation
- Used expect() instead of unwrap() for better error messages

* refactor: simplify parse_proxy function

- Remove redundant comments
- Extract server variable to reduce duplication
- Inline trivial username/password variables

All 7 proxy tests still passing.

cli/src/flags.rs

@@ -10,6 +10,7 @@ pub struct Flags {
     pub executable_path: Option<String>,
     pub cdp: Option<String>,
     pub extensions: Vec<String>,
+    pub proxy: Option<String>,
 }
 
 pub fn parse_flags(args: &[String]) -> Flags {
@@ -28,6 +29,7 @@ pub fn parse_flags(args: &[String]) -> Flags {
         executable_path: env::var("AGENT_BROWSER_EXECUTABLE_PATH").ok(),
         cdp: None,
         extensions: extensions_env,
+        proxy: None,
     };
 
     let mut i = 0;
@@ -67,6 +69,12 @@ pub fn parse_flags(args: &[String]) -> Flags {
                     i += 1;
                 }
             }
+            "--proxy" => {
+                if let Some(p) = args.get(i + 1) {
+                    flags.proxy = Some(p.clone());
+                    i += 1;
+                }
+            }
             _ => {}
         }
         i += 1;
@@ -81,7 +89,7 @@ pub fn clean_args(args: &[String]) -> Vec<String> {
     // Global flags that should be stripped from command args
     const GLOBAL_FLAGS: &[&str] = &["--json", "--full", "--headed", "--debug"];
     // Global flags that take a value (need to skip the next arg too)
-    const GLOBAL_FLAGS_WITH_VALUE: &[&str] = &["--session", "--headers", "--executable-path", "--cdp", "--extension"];
+    const GLOBAL_FLAGS_WITH_VALUE: &[&str] = &["--session", "--headers", "--executable-path", "--cdp", "--extension", "--proxy"];
 
     for arg in args.iter() {
         if skip_next {