README logo doesn't render on PyPI (relative image path)

## Problem
The OWLAPY logo at the top of the PyPI project page (https://pypi.org/project/owlapy/) doesn't render — see screenshot in the linked conversation. The rest of the README (badges, text, links) displays fine.

## Root cause
`README.md` line 11 uses a repo-relative image path:

```markdown
```

This resolves correctly on GitHub (relative to the repo root) but PyPI renders `long_description` standalone with no base URL to resolve relative paths against, so the image link 404s silently there.

## Fix
Point the image at an absolute URL instead, e.g. the raw GitHub content URL pinned to a tag/branch:

```markdown
```

(Pinning to `main` means the image can still change without a release; pinning to a specific tag guarantees it matches what shipped, at the cost of needing an update each release. Worth a quick decision either way.)

## Scope
- Fix `README.md`'s logo line
- Check for any other relative asset links in the README that would have the same problem
- Verify by re-checking the rendered `long_description` on the next PyPI upload (`twine check dist/*` doesn't catch this — need to actually view the rendered page, or use `python -m readme_renderer README.md` locally)

Start with README.md line 11 and inspect the README for other relative asset links like docs/_static/images/owlapy_logo.png. Choose whether the image URL should track main or a release tag, update the affected links, and use python -m readme_renderer README.md or inspect the next PyPI-rendered page to verify the logo displays.

Written by the indexing model from the issue text.