[codex] Add duplicate submission URL validation

[TSS99]

Summary

• add a checker implementation for existing check 011 so duplicate submission URLs are flagged
• recurse through package and PyPI URLs when validating submission URLs
• add unit tests covering duplicated website URLs and nested URL collection

Root cause

Check 011 already existed in resources/checks.toml, but it had no checker attached, so repeated submission URLs were never enforced. On top of that, the URL collector in ecosystem/validation/test_url.py only looked at shallow top-level fields, which meant package and PyPI URLs were skipped entirely.

Fix

• implement duplicate URL detection in ecosystem/validation/test_url.py
• normalize URLs before comparison so trivial formatting differences like trailing slashes do not bypass the check
• include member.pypi.*.url in check 011 metadata
• add focused unit tests for GitHub/PyPI duplicate website cases and nested package/PyPI URL traversal

Tests

• python -m pytest tests/test_validation_url.py -q
• python -m pylint ecosystem/validation/test_url.py tests/test_validation_url.py
• python -m black --check ecosystem/validation/test_url.py tests/test_validation_url.py
• inline validate_member() sanity check showing the duplicate-URL case fails on test_url.py::TestURLs::test_duplicate_urls while a distinct-URL case passes cleanly

Notes or limitations

• I did not run the full repository test suite because upstream tests/test_check.py currently has a syntax error on main, unrelated to this patch.
• The targeted pytest runs emit a local requests dependency warning about the installed urllib3/chardet combination, but it did not affect the checks above.
• AI assistance disclosure: OpenAI Codex (GPT-5) was used to help prepare this contribution.

Fixes #1087