feat(init): allow manim init project into an existing folder

[Chessing234]

Summary

• manim init project refused to run whenever the target directory already existed, breaking the natural flow suggested in Allow manim init project into existing folder #4693:

  uv init . --bare
  uv add manim
  uv run manim init project .

• Now it only refuses when a file it would create (manim.cfg / main.py) already exists in the target folder; otherwise it initializes into the existing folder (creating it if needed).

Closes #4693

Test plan

• pytest tests/interface/test_commands.py -k init
  • test_manim_init_project_existing_folder — initializes into a pre-existing, non-conflicting folder
  • test_manim_init_project_conflicting_files — refuses and leaves an existing main.py untouched

Made with Cursor

[GniLudio]

I think it should be possible to even target folders with conflicting files, by just overriding the existing file(s).

[Chessing234]

Good call. I've updated it so a conflicting manim.cfg/main.py now prompts for confirmation and overwrites on "yes", rather than refusing outright.

I kept a prompt (defaulting to no) instead of overwriting silently, since init project . is easy to run in the wrong directory and could clobber someone's work. If you'd prefer it to just overwrite unconditionally, I'm happy to drop the prompt.