New edit tool

[stippi]

This one doesn't use

>>>>>>> SEARCH
text to replace
=======
text to replace with
<<<<<<< REPLACE

diff blocks, but two separate old_text and new_text parameters and optional replace_all like Claude CODE uses. I saw way too many tool failures, when the LLM attempts to create diff blocks with multiple search/replace blocks. The old replace_in_file tool is still available via CLI toggle.