test: cover NavLink trailing-slash active-state edge cases

[Favourejiro]

closes #321

adds RTL coverage for NavLink's active-state and aria-current behaviour.

src/components/NavLink.tsx computes an active class and sets aria-current="page" from useLocation().pathname. This is the primary
navigation affordance, and its active/current logic is exactly the kind of thing that silently breaks on a router upgrade. This PR adds
focused tests for that logic under MemoryRouter, including the trailing-slash edge cases called out in the issue.

What's covered

All tests render NavLink inside a MemoryRouter with controllable initialEntries:

• Active match — when to matches the current path, the link has the active class and aria-current="page".
• Non-match — on a non-matching path, the active class is absent and aria-current is undefined.
• Prop forwarding — className and ariaLabel are forwarded to the rendered link.
• Trimmed class string — no leading/trailing spaces (verified for empty-className + active, and empty-className + inactive).
• Root vs non-root matching — / is active only on the exact / path; non-root links use prefix matching.
• Exact vs partial path match — a nested path (/vaults/123) activates /vaults, while /vault does not activate /vaults.
• Trailing-slash differences — to="/vaults/" with path /vaults stays inactive; path /vaults/ activates to="/vaults".

Testing

npm run test -- src/components/tests/NavLink.test.tsx

✅ 12/12 tests pass. No source changes — test-only, no regressions to navigation highlighting.