fix(browser): add missing PressKeyAction dispatch case

[wangwangbobo]

Summary

Fixes PressKeyAction silently failing with "Unknown action type" error.

Root Cause

The press_key() method was fully implemented at line 513 but never wired into the dispatch logic. The browser() method jumped from TypeAction directly to GetTextAction, skipping PressKeyAction.

Fix

Added 2-line dispatch case between TypeAction and GetTextAction:

elif isinstance(action, PressKeyAction):
    return self.press_key(action)

Testing

• press_key() method already exists and is correctly implemented (lines 513-533)
• PressKeyAction is already imported and defined in models.py
• This is purely a missing routing case — the handler code was already there

Fixes #350