fix: make README discovery case-insensitive without Path.glob case_sensitive

[mtran-code]

• Root cause: using Path.glob(case_sensitive=...) causes TypeError on user environments.
• Fix: perform filename-based case-insensitive matching via iterdir in root and docs.
• Tests: added tests covering root and docs case-insensitive README detection.

Fixes #8

[mtran-code]

Closing in favor of Python 3.12+ requirement PR.

[mtran-code]

Reopening to prefer this change over the 3.12 dependency bump.

Don't wanna mess with dependencies in case some other packages need 3.11.

[mtran-code]

@strixy16 This is the new PR, It wasn't merged but feel free to review with the original issue if it makes sense and merge if it looks good.