fix(scope): warn on empty scope segments

[wananing]

Flag repeated, leading, or trailing slashes in scope linting by detecting empty path segments.

Fixes #56.

Summary

Make scope linting report malformed scopes that contain empty path segments, such as acme//pay.

Solution Description

• Detect empty scope path segments by checking scope.split("/").
• Emit a lint warning for repeated, leading, or trailing slashes.
• Add a unit test covering _lint_scope("acme//pay").

Verified with:

• uv run ruff check src/ tests/
• uv run ruff format --check src/ tests/
• uv run pytest tests/ -q

[Evenss]

LGTM