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.

src/protocol.ts

@@ -19,6 +19,17 @@ const launchSchema = baseCommandSchema.extend({
     .optional(),
   browser: z.enum(['chromium', 'firefox', 'webkit']).optional(),
   cdpPort: z.number().positive().optional(),
+  executablePath: z.string().optional(),
+  extensions: z.array(z.string()).optional(),
+  headers: z.record(z.string()).optional(),
+  proxy: z
+    .object({
+      server: z.string().min(1),
+      bypass: z.string().optional(),
+      username: z.string().optional(),
+      password: z.string().optional(),
+    })
+    .optional(),
 });
 
 const navigateSchema = baseCommandSchema.extend({