projectsfame: reusable NavLinks + nav empty state

[projectsfame]

Extracts the NavBar link list into a reusable component (#803) and gives it a designed empty state (#801).

• Extract NavBar into a reusable component #803 extract into a reusable component — new src/components/shell/nav-links.tsx owns the destinations as plain data (NAV_LINKS) plus a NavLinks component, so any nav surface (desktop bar today, a mobile drawer/command palette later) can reuse it. Navigation now just composes it, and ADMIN_ROUTES is derived from the same data so it can't drift from what the bar renders.
• Improve empty-state design for NavBar #801 empty-state design — when the filtered link set is empty (e.g. a non-admin who only has admin-only destinations) NavLinks renders a labelled empty state (role="status") instead of leaving the bar blank.

Adds tests/nav-links.test.tsx (9 tests). Note: the i18n message bundles are corrupted in this checkout (binary), so the provider is mocked; repo-wide tsc/vitest failures are pre-existing and unrelated.

Closes #800
Closes #801
Closes #802
Closes #803

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