Regression tests for share path coverage and avoid_list

[blinkerbit]

Source: gitlab-issues-export.md (Issue 5)

Weight: 2

Problem / context

Past reviews flagged static-share avoid_list interactions with path coverage. Logic in share_covers_relative_path was adjusted; coverage should be locked in tests to prevent regressions.

Suggested approach / acceptance criteria

• Tests in tests/test_database_shares.py (or adjacent): static + dynamic + tag shares with avoid_list / allow_list ensuring excluded files are not served as in-share.
• Include at least one direct file URL style relative path if applicable to handler routes.