feat: add mini.files support

[jdurand]

Summary

• Extends file manager integration to support mini.files
• Support both visual selection and single file under cursor

Changes Made

• Added _get_mini_files_selection() function to integrations.lua
• Added mini.files filetype detection in get_selected_files_from_tree()

Builds on the netrw support PR and extends claudecode.nvim to work with the mini.files file explorer.

Bonus

Fix openDiff blocking operations failing in test environment due to
incorrect coroutine context detection. In Lua 5.4, coroutine.running()
returns (thread, is_main) where is_main indicates if running in main
thread vs coroutine.

Changes:

• Update diff.lua: Fix open_diff_blocking coroutine check
• Update tools/open_diff.lua: Fix handler coroutine validation
• Update tests: Add proper mocking and expected error messages

[ThomasK33]

Hey @jdurand, thanks for the PR.

Could you please format the code with make format?

Could you also add a test fixture for mini.files in the fixtures folder?

[jdurand]

@ThomasK33 I added the fixtures based on the structure you set up, but I wasn’t able to use them on my local env. Let me know if that works for you.

[ThomasK33]

Apart from some dead or unfinished code, LGTM.

[proofer]

Heh. I just opened this repo to do a search on "fixtures" and found, along with the dev info I was seeking, this PR. I'm within a day or two of submitting the same PR to accommodate my being a longtime user of mini.files, which I'm now using with claudecode.nvim. I'll take this opportunity to say that I've been amazed by the engineering skills of @ThomasK33 et al. on display in this plugin -- I've learned a lot. And also, just as a user of Claude Code, thanks for the plugin!
Edit for P.S.: Thought maybe I should be explicit: I won't be submitting my mini.files support PR, but if there's anything I can do please let me know!