Add iframe support for click/fill/type commands

[mehmetnadir]

Description

Currently, click, fill, and type commands only work on the main frame. Elements inside <iframe> are not accessible.

Expected behavior

cdpilot click --frame "#my-iframe" "button.submit"

Implementation hints

• Use Page.getFrameTree CDP method to list frames
• Use Runtime.evaluate with contextId for the target frame
• Add optional --frame <selector> flag to interaction commands

Files to modify

• src/cdpilot.py — cmd_click, cmd_fill, cmd_type

Good first issue — straightforward CDP API usage.